Depends on your electrical system.. If it's solid with a good aftermarket alternator and an upgraded battery, a cap has the potential to do some good.
When you put a cap on a stock system, whenever the cap discharges it'll drain the battery to recharge itself. That'll cause extra strain on the battery and the alternator, and can cause them to go out pretty quick. Could possibly even leave you stranded.
As for amps, see if you can find a Tsunami 1800.. It puts out max power at 2ohms, but might be a little overkill. If you're easy on the gains, then it should do a pair of 12s every bit of justice, and then some.
Check around at
www.ikesound.com ,
www.sounddomain.com , and
www.thezeb.com
If you see an amp that claims 1000watts, but costs under $200, don't buy it. You get what you pay for, and you want to send some good clean power to those subs.
Also check out
www.caraudioforums.com and do some poking around in the amplifiers section. If you have a question, use the search feature first of course.. If you don't find what you need, go ahead and ask. Most of those guys don't mind answering questions.
Goodluck.