I plan on buying 2 avalanche. So I will need one big amp to push both sub or 2 amp. Which I still don't know what amp's I am going to buy. Maybe a ppi or jbl? Also should i run 4gauge or 0gauge? My Alternator is 160amp would i need to replace that? I will need to replace the battery should i buy the red top or yellow top? 1 or 2 batteries?
One amp will do just fine. You can look at Zapco/Arc Audio/US Amps/JL if you have the money, or PPI PC/PCX series amp, JBL, Orion HCCA for mid to low priced amps. If that's still too high, then look at MTX/Audiobahn. You should be okay with 160A alternator for now. You don't have to replace the battery unless it's dead or plannning to listen to the car audio with the engine off.
Zapco's C2K 6.0 for class AB, or C2K 9 for class D. They're both expensive but well worth it. JL 1000/1 is a nice amp, costly still. 4 gauge is the minimum with these amps. 0 gauge will be a better choice.
What is the power of your subs? It'll depend on that. If they are 500w rms each or close to it, then yes, JL 1000/1 amp will be able to drive them both. If it's higher, like 800w - 1000w each, then look at Zapco's C2K 9. US Amps make very good amps as well. Try looking at their website.