I've got a 1500W amp going in my Sunfire and need to know what gauge wire to use for everything, which of the deep cycle batteries I should buy, which farad cap, and who does cheap alternator upgrades. Would 160-180A be enough?

 

Do 1/0 wire for power/ground, 10-12 gauge speaker wire, get a yellowtop/odyssey/kinetik/whatever battery, and yeah 180amps for 1500watts will probably suffice with the help of a deepcycle... and forget the cap.

 

Do the big 3 too.

 

Do a big 3 upgrade. On a Sunfire it's cheap and quick.
If the battery is getting old replace it with a better unit. If it is still in good condition just leave it until it's due to be replaced unless you really plan on running your system for extended periods with the engine off but if you do plan on doing this you may want to look into a second battery to aid in this.

I have a 180a+ hot rated alt on mine with the voltage turned up a bit with a constant being held easily at 14.8v. For your 1500rms amp and with it the requirements of a modest full-range amp a 180a alt would be plenty. I would recommend using the money you alotted for the cap to buy the biggest alt you can get. I mean if the money's there you might as well buy big and it will leave you with that much more room to go really big on power amps if you decide to in the future.