I'm gonna start saving up for a good quality metal amp that can do "teh brutals". From what I've seen and read, one of the 5150s/6505s is looking like the best option without spending a ton of money. Or should I look at something else?

What will the warranty on a new amp cover, or should I just look in the used market?

I know a lot of people recommend combo amps over stacks, is it still a better option over a decent cab?
Combo vs cab is just a matter of, do you want to carry around, a head, then a large cab, or the both put together.

Peavey is an awesome company for metal amps, if you buy from like guitar center, you can buy a warranty, but still used is still good. The only thing you want to watch out for is the tubes, if you buy a used amp then have to spend a hundred or so dollars reaplacing tubes it might be worth it.