tay12lex Thing is for the price of those amps and a decent distortion, you could just get a good amp to begin with, especially with the rise of small amp heads. 
I can't imagine 0 gain would be conducive to a good tone...

Honestly, without knowing the amp and what you're aiming for, it's impossible to say. In addition, it'll be affected by your guitar, your playing, the room you're playing in, your hearing and a whole host of other factors. Play around with the setting and find what works for you.

The only general advice I'd give would be to dial your tone with the volume and tone on your guitar dialed back a tad. It pretty much gives you a controllable boost at your fingertips and can help maintain definition even with higher gain.
If it fits within budget, a Peavey 5150/6505 is kind of the gold standard for that sort of metal. However, the cleans are pretty meh at best. Another one to look at would be the Randall RD20, great distortion but really nice cleans too.
Why specifically a Marshall? What budget? Location?
If you want good cleans, avoid the 6505/5150. That said, it's a gold standard for metalcore. Depending on how the used market is where you are, possibly look at a used Rectifier or Mark series. You could also fit a Kemper and powered cab into that budget.
Especially for metal, I'd consider a good modelling setup in that price range, something like a Helix and powered cab.
No more awkward than playing 6 string songs on a 7. Once you get used to the neck, there's no real problems.
Out of those, probably the Schecter. What's your budget and location? Are there any features you do/n't want on a guitar?
Really depends on what you're wanting to do. I'd say a compressor and overdrive are the most universal though.
That's just using a jack for the footswitch right? If so, pretty much any generic one should work.
For me, I'd get a delay and an overdrive. However, I think delays generally sound like ass going through the front of an amp and an overdrive would't do much for a modelling amp like your Spider.

What you really need is a new amp. Then you need to figure out what you want to achieve.
Define work. You could probably tune up just fine, but they might be really tough to play.
Sounds a LOT like a really distorted bass, not a guitar.
Really depends how your amps channels are controlled. I use a Boss ES8 for this function, although there is a slightly smaller one too. Would be MUCH easier if my amp had MIDI though.
Might be a tiny bit over budget, but a Randall Diavolo might have what you want. You'd want at least the 20w version if you're playing with others. Great distortion, really nice cleans for a metal amp. For portability, you'd want to pair it with a 1x12 cab at most. The head is light and small enough to not be a problem to transport.

For something portable, have you considered a modelling setup? If the spaces you're going to have speakers or a PA, they're a lot easier to carry and more consistent in tone.
Do you feel there's anything lacking in your tone? Those amps are really solid for mid gain tones and earlier metal, you got a really good deal for that price. That said, it wouldn't be my first pick for 90s metal. Nor would be the Tiny Terror, although it's certainly closer to that sound. If you aren't using the modelling features of the Vox, it would certainly be an upgrade.

What's your budget and location?
I'd let someone with better knowledge of acoustics chime in here.

However, beyond just the physical dimensions, I'd imagine the vertical might be a bit better for monitoring, as it'll be closer to head height. However, the horizontal one could let you play around with a stereo rig if you got another amp down the line.
The Randall is actually really versatile, especially for a metal amp. Only complaint about mine was the single shared EQ between the two channels. However, great cleans and pretty brutal distortion that still has some definition.

1300 euros opens you up a bit. For stacks, it's worth looking at the various Victory amps and a few Engls. You might be able to get a used Mesa in that range too, although I'm not too well versed on the used market in Europe.

At most gigs, you'll be miced up anyway, you don't actually need a crazy powerful amp. However, modern guitar amps are obscenely loud even at low wattages. A vintage 30 is rated at 100dB at 1w. I'd advise against a 4x12 unless you have someone to lug it around for you. Every piece of gear you have is another thing you'll have to set up, break down and transport. 
It really depends on what you're trying to achieve. In the past, I used them at the end of my chain just before the reverb and delay. At this spot, it was to slightly tweak the overall sound more to my taste. I did also like using one as a solo boost at times, when used like that I used it right at the start, with only the volume pedal before it.

EQ is a lot like a noise gate, where you can place it pretty much anywhere depending on what you're wanting to do.
What sort of budget and genre are you looking at? Assuming you're looking at a gig worthy metal setup, there's quite a lot under 750 euros. If you got the 2x12 vintage cab, it's worth checking out the PRS MT15, Peavey 6505 MH, Randall RD20 and Joyo Mjolnir. If you don't mind a combo, I'm pretty certain you can get a 6505+ combo or Line 6 DT25. 

I've used the Harley Benton cab for almost a year now, first with a Randall RD20 and now with a Mark V (alongside a Mesa 1x12) and have zero complaints. I'm sure a better cab would improve the sound, but it still sounds great.
duncandisorder So funny enough, I actually do Metallica covers. My main rhythm tone goes guitar > Boost/gate > Volume > Wah > Mesa Mark V > Chorus > Delays > Reverb > Speakers. There's a tuner built into the POD and both the POD and ES8 both have mute buttons built in. Whole thing is controlled from my Boss ES8, so I don't need to pedal dance. It controls channel switching and my overdrive directly and controls my POD through MIDI and I think something like that is borderline mandatory if you run a lot of effects. 

Since you aren't using that many effects, it may be worth going with just a couple individual pedals. Maybe just a Wah, Overdrive/boost, chorus and reverb.

Chorus and reverb are two totally different effects. A reverb simulates how sounds are affected by space. It can make it sounds like your amp is in a much larger room than it's in, or in a cave, or a church or pretty much any space you can think of. It can help make your sound stand out a bit, especially if you're the only guitarist.

Chorus tries to emulate additional instruments being played at the same time. As with a choir of singers, even if they're singing the same thing and have similar voices, there are tiny differences in timing and pitch. In practice, it helps to make your guitar sound bigger than it is. Particularly on clean tones, it fills out nicely. 

Here's a couple of videos explaining how they sound:

Looking online on Boss's website, it looks like you should be able to use it as an audio interface no problem. However, it doesn't even have an XLR input, let alone a mic preamp, so you could not use a microphone with it.
Whats the chain like in the patches you use? Is it just guitar > amp > cab or do you have other effects running too? A bit of reverb is pretty essential if you're playing through headphones imo, and a boost and a tiny bit of chorus cuts through nicely.
If your EQ is all at 5, try playing around with that. Also, it sounds like you're physically playing pretty softly. For overdriven stuff, don't be afraid to put some more power in your playing.
In addition to the string tension (which you can somewhat get with a baritone) the pickups are often made with the lower notes in mind. They help keep some of the brightness, which helps a lot with clarity and being heard in the mix. Here's a video showing the difference, albeit on an 8 string:

The other thing is quite a few djenty dudes like playing with arpeggios on the higher strings. An extra high string opens up chord and arpeggio opportunities.
A combo is just a cab with a head integrated into one unit. It's very rare there's much of a difference beyond that tbh (For example, the 6505+ combo apparently has some issues with the FX loop that aren't present on the head.) 

Generally, a head makes it easier to choose between cabs and speakers at the cost of being a bit more fiddly to set up and often being more expensive. The whole setup is often a bit heavier, although you can at least move it in multiple pieces. 
esbaltaci1231 You would need to buy an audio interface with a instrument level input. Something like this for example:
esbaltaci1231 An effects loop on a multi FX unit just means you can add external effects to the chain, it's not required to be able to use a MFX with an amp, although I certainly think it's useful. With a lot of newer units, you can control exactly where the loop is placed. For example, say you wanted to add a chorus. Without a loop on the multi FX, you could only add it at the very start or very end of your chain, neither of which are often where a chorus is used. With the FX loop, you could place it after your distortion but before the reverb and delay. 

It's pretty much the same deal with the effects loop on an amp. Without it, you'd have to use the MFX right at the start, which is fine for some setups and genres but unusable in others. If you have an effects loop on the amp AND the pedal, you can do some interesting things. First, it lets you have effects both before AND after the preamp. For example, most metal players use high gain amplifers for their distortion. A typical setup might go Wah > Overdrive > Amp > Delay > Reverb. Without an effects loop, you'd have to run everything in front of the amp. Problem is time based effects like delay and reverb don't always sound that great there, especially when using a lot of gain. I actually use this setup myself with my Mark V.

The other thing is to bypass the preamp all together. Obviously this only works when you have amp modelling on your MFX unit. Let's say you have a Peavey 5150. Killer amp with fantastic distortion, but some of the worst cleans in the world. With your MFX, you could ignore that preamp and instead use the model of a Fender Twin or a Roland Jazz Chorus and enjoy fantastic cleans while still having the brutal distortion of the 5150. The opposite is also true. Take a Jazz Chorus, get something with a convincing Dual Rectifier model and you'll have a solid metal sound.

TL;DR: You don't need an effects loop to use a multi FX unit, but there's so much you can do with it that it's well worth having.

EDIT: The placement mentioned here is only one way of setting up effects. Even the stuff I said should be avoided has been used to great effect. There are rules of thumb, but those are made to be broken. Someone has successfully used pretty much any combination of effects you can think of in any order. 
What you really need is a new amp.

Meme aside, what exactly are you trying to achieve? Are you trying to compensate for things your amp is poor at or do something your amp can't do? If you're making up for a bad amp, then getting a better amp seems the logical choice. If you want new sounds, then look at the gear that'll give you those sounds.

If you're unsure, I'd recommend just picking both and getting a quality multi fx unit. It'll give you a wide range of tonal options and would be great for a quiet rig.
Quote by theogonia777
It might be a good idea to start off with a multi-fx so that way you can play around with a variety of different effects and get a feel for what you like.

This is good advice too. My current rig actually uses a POD HD500x for most of the effects, as I used to run a pure modelling rig. Now I have a separate overdrive and will have a separate delay soon and that's all running through my Mark V. Only real rule is there are no rules!
Depends a lot on the specific pedals in question. As a VERY general rule of thumb, single pedals are often better than a multi fx at the expense of expense (heh), space on your board and quantity of cables. However, you also get fantastic multi fx units and shitty single pedals, so YMMV.

Pedal order is quite important and one could write an essay on this subject alone. For example, if you had a distortion and a delay, did you want to add delay to your distortion or distort your delays? The sound will be different on both of those and neither is "wrong". The kinda accepted order would be something like Tuner > Dynamics (Compressors) > Wah > Distortion/Overdrive > Modulation (phaser, Chorus etc) > Time (delay, reverb) with a noise gate and EQ sprinkled in where needed, but I guarantee the next few posters will have disagreements with this order. Pretty much the only thing people will all agree with is tuner at the start.

If you get the chance, it's well worth experimenting and seeing what you like.
addman3455 yeah, that sound is just the guitar itself. Crank it up and it should go away. The iPhone mics are pretty sensitive, so distance doesn't always help.

I uploaded a clip demonstrating the sound here:
Could you show us a clip of what's happening?
Quote by Deadpool_25
The Boss ES-8 (and I assume the ES-5) can do what you want easily. It has the ability to run loops in parallel.

Came here to suggest this.
Any idea for what exactly? You've posted 3 guitars but you haven't said why you're choosing between those 3.
The advantage is not having to sacrifice the higher notes in those low tunings. In addition, a lot of 7/8 string pickups are made with those lower notes in mind, which can help with clarity compared to some 6 strings pups.
Really depends what sort of sound you're after. I have the Distortion in my 6 string. It's great with a bit of gain, but the cleans are pretty poor. The JB I remember as a bit more dynamic with better cleans, but a bit less in your face aggression. Both are great for metal but they do offer different sounds.
There's pros and cons to a floyd, it comes down to whether the pros outweigh the cons to you.

+Whammy tricks
+Great tuning stability when set up
+Fine tuners great for... fine tuning adjustments

-String changes and setups take longer
-Any tuning change WILL require a setup
-Cheaper Floyds often suffer from stability issues

I think they're great fun, but unless I had something like a Variax, I don't think I'd want one on my main axe.
mesaboogieman Unfortunately, I don't really do much in the way of modifications on guitars, so I couldn't advise you on the best approach. I can confirm that a guitar set up for that tuning won't be suitable for less extreme tunings without additional setup.
Monstrously thick strings are indeed the way. On my 8 string, I use a 74 for the low F# on a 27" scale length. A 56 is barely enough for a low B imo.