if you want a fast car, huge soundsystems are counterproductive. i love when i see kids with like, carbon hoods and shit, then a 300lb box/twin 12s setup in the back. fucking retards. and if you are gonna get a system installed, find some peeps who know whats up. if your in ohio, i know 2 buddies of mine that do truely amazing work. they are way into acoustics, and thier enclosures, and electronics are amazing.
also, now, as for a car, if you have to ask what i should buy, you need to hit the books, test drive, and figure shit out yourself. as someone else said, everything your talking about is insainly different. if you want to get into serious sport cars, and your comming from a neon, drop a few grand on a smaller rwd car. my bud (same one with the sound company) bought a wicked nice lil Porsche 924 turbo for 2500. its not wickedly fast, nor is it gonna kill you. itd be a very good investment to learn to drive a sporty, rwd car before getting something like an RX7 or supra, which you would just crash. if your looking for a fast daily driver, anything all wheel drive is going to be much nicer than rwd, specially for snow and rain. audis, subs, evos, golf/rabbit r32, whatever.