Hello there.

I've got an Epiphone g-310. Guitar is good, but, of course with a lot of things which could have been better. I've been planning on doing a major customization of my SG. But sometimes I hear such things like "Don't bother yourself and just buy a good guitar (Gibson, Fender, Gretsch etc.)". So I decided to ask those experienced, what do you think about it? Should I upgrade my Epi or buy something more decent?

Here's the list of modifications I would like to do:
- change the whole electronics and pick-ups (Seymour Duncan SH-1 59)
- polish all the frets
- install bigsby tremolo bridge (or something similar)
- changing the color (maybe)
-??? (Maybe you can offer some other useful or just cool mods )

Thanks for attention
If you really like the guitar, I would do all those mods except the refinish. The thing is, unless you spend a lot more on a new guitar, you aren't going to get as much performance benefit as you will from changing the pickups and maybe electronics. The downside is that you won't recover the value of the mods on resale. To partly offset that, I would keep the old pickups, and put them back in if you plan on selling it. Sell the SDs separately if you don't want them for your next guitar.

I would only do the refinish if I enjoyed that kind of thing as a hobby in itself. - It will reduce the resale value guitar.
I have a ton of respect for you saying " Don't bother yourself and just buy a good guitar (Gibson, Fender, Gretsch etc." so many people will just say that and move onto the next thread.

if you like the sound of the guitar go for it. I mean all the high end parts you're thinking of putting you can put onto other guitars but find out what the guitar is missing and go from there if you see the need to upgrade the guitar. I tell guys to get a processor before upgrading a guitar first. But anyways for the sake of doing project guitars.

CTS or bournes potentiometers
250k pots for single coils
0.022uf capacitors for single coils - i wouldnt pay too much attention on capacitor material
500k pots for humbuckers (250k on humbuckers will be too dark)
0.047uf capacitors for humbuckers - its a bigger difference in tone knobs (or use 0.033uf)
wire is wire but if you need it 24awg wire from an electronics surplus store (single stranded is easier). Some will argue about wire material but it's up to you.

push pulls , mini toggles. Lots of in between stuff comes to mind as well for wiring mods. I'm thinking of doing a blog on every wiring mod I know. Tell us about the guitar and I'll have some ideas for you.

polishing the frets is easy - the best results I suggest micromesh and polish up to 12,000 grit. Use some tape on the fretboard to make sure you don't scratch the fretboard though.

painting / refinishing a guitar costs a lot of money. 200-ish dollars in canada which will buy me a really nice used Jackson pro series or mid ranged LTD at the end of the month

pickups worry more about the sound of what you'll get instead of going with a big name. The regular alnico pro II before slash got a signature pickup , the seymour duncan jazz and a bunch of others exist to give you that vintage sound. Personally I go high output and then with wiring mods wind it down to "vintage".

for the bigsby there is a bunch of different models make sure to get the right one. The cheapest was on amazon.com for like 70$ american. But stetsbar, kahler, floyd rose FRX (very expensive) and a bunch of others come to mind that will do what you want it to.
One of the joys of upgrades is you can do them bit by bit, as you can afford them, and each upgrade makes a difference.

You also understand, and appreciate the value of each upgrade. You may well spend more on a cheap guitar (which will never be more than a cheap guitar) than a "quality" guitar with the same components - but as it is over a period of time it doesn't seem as much.

All logic says "just buy the quality guitar". You may even do that in the fullness of time. However, you will have the advantage of knowing and appreciating all of the components that go to make up that a quality product.

I am a cheapskate - I will frequently endeavour to save money by going the upgrade route. This, very often, turns out to be more expensive and I even ultimately end up buying the "quality" version of what I have tried to replicate on the cheap. However, my journey has been worth the expenditure and I end up feeling sorry for those who bought the quality product first as they can't possibly appreciate all of its subtle joys as I do.

There is the "Buy cheap - buy twice" and this is often true. But, being able to really appreciate something is perhaps worth that bit extra.
Thank you all for such great answers .

Well, maybe mods will cost more than guitar itself, but buying a decent guitar is even more expensive, because in the future, as my skills and style will progress, I will also modify it.

I can't tell a lot about my SG. I mean, not more than the official website tells us.

Body mahogany
Neck mahogany, bolt-on
Scale 24.75”
Neck Profile Slim-Taper™ “D”
Nut width 1.68
Fingerboard rosewood, 22 fret
Fingerboard Radius 12”
Neck Pickup 650R humbucker
Bridge Pickup 700T humbucker
Bridge LockTone™ Tune-O-Matic
Tailpiece Stopbar
Controls Neck pickup 1-Volume, 1-Tone, Bridge pickups 1-Volume, 1-Tone with full-size 500K O potentiometers
Hardware Nickel
Tuners Premium die-cast
Color Ebony

Oh, right. Inspite Epiphone tells us that it is not neck-heavy, it astually is. That is pretty annoying and I have heard a lot of advices how to fix it, like:
- wide leather strap (most popular fix but I don't really like that option)
- replace the strap button on the tip of the horn (I've been thinking about it, althoug it is risky but it will also make reaching low frets more comefortable, because now they are a little bit too far).
- put some BBs in the section with electronics https://www.youtube.com/watch?v=xOsjORziFoc (this solution also have intrigued me, but I am not sure if it is safe and will not affect the tone, so, what do you think about it?)
- install a tremolo (I really like tremolos like Bigsby, they suit my style, so I find this solution pretty good).

Found on the internet Les Trem II tremolo. It is cheaper than Bigsby and seems solid. Does anybody have experience with those?