Running that much power, a cap is a really good idea, especially in a 4 cylinder, foreign car. The alternator in your car, although it does have some reserve, isnt really made for that kind of current draw, and you'll definatly have problems with the lights dimming and all. Also, make sure your alternator is up to snuff... Autozone usually will test them for free, if its an older alternator, its a good idea to have it checked. All that current draw can kill it.

as I said before, you may want to invest into another sub amp, or drop one of the subs... the infinitys need a lot of power to do their job efficently. The amp will be fine, you will just seriously shorten the life of the subs by under powering them.

RCA cables are not hard to make... just a matter of soldering the RCA connectors on the ends pretty much. The only down-fall is that they are not "siameesed" in pairs... so you'll have a bunch of single cables to hide. Plus, microphone cable is rather large in diameter compared to interconnects made for the car.

Speaker cables are just a matter of stripping the ends.. or if you get the twisted pair cables, there is usually a "cap" that goes at the end to make for a neater install. You can use connectors on the ends too, such as bananna plugs, spades...etc, but to me its not worth the money, unless you want everything to look its best.

I personally say stinger because they make EVERYTHING you need or could want... and I can get good prices, but their prices are pretty reasonable to begin with.