I want to get an epiphone VJ, but I've got a couple options. I either get the combo, or the head and I build a cabinet. Which would be better/cheaper? Is there anything better about the heads amp over the combos amp? Anything I can't easily mod back in?, because I'm planning on doing some serious mods to it. Thanks!
I am going to build a cab when I get a VJ. I am going to use Eminence drivers from partsexpress.

I have built many audio speakers and a guitar cab is about 80% easier to do. There is no cross-over to build and the cab deminsions are not "as" important. I think it is a better option because you will get a cab for about the price of a low-end model but it will have better components, construction, and sound.

Take it for what it is worth but I would go for it.

well how much would it cost to build a cab? Would I want a 4, 8 or 16 ohm speaker? Are there any components to a cab apart from the speaker? I mean, you don't have to plug the cab into anything but the amp right? So are there other passive components I'd need? I've only ever played through combos.
youll need an input jack for the cab and wiring and stuff to solder with. You cant say how much it costs becasue you could spend anywhere from 200 dollars to 2000 dollars on speakers.
Quote by ILuvPillows?
Masturbate it off.
Also, the speaker you choose will determine the oHms.

Truth to tell, if you get creative and think ahead, you could have inputs for 4, 8, or 16 oHms but that involves at least searching for scehmatics and the "how to" so you can have some resistance to handle the differing load from the canned speaker oHm's. I am going to do this simply because I want the cab to be useful for other amps if I should choose to buy another in the future.

What are the advantages/disadvantages of different impedance speakers? If you had an amp looking for an 8 ohm load, could you put a 4ohm speaker in series with a 4ohm resistor? Or vice-versa and put the resistor in parallel? What does it all mean?
I would do some searching on here and Google. I am sure you will get some links and/or pictures (schematics) to help.

You are on the right path though. If you have, lets say, a 2x12 cab, wiring in series or parallel is an option to change the load. Again, if you are aiming at a certain impedance, the speaker selection will help you to make those decisions.

I'd settle on a driver (speaker) first, then go from there.