Don't know much about building bottom ends but with your question on the rear clip, if you're going to get an aftermarket or "cooler" rear bump, you can always buy those separately, but the thing is, it'll look weird with the rest of your car if your tail looks great while the side skirts and front are stock.

Nowadays the cool thing to do is a lip kit, which uses stock bumpers and skirts and adds a subtle flair. To buy these things, I'd be patient and keep watching the HAN classifieds, honda-tech.com classifieds, and the team-integra.net buy/sell forum. People always throw up parts at ridiculously low prices and you'll save anywhere from 50%-75% off. I'm an example, I bought a DC 4-2-1 ceramic header for $60 because some guy was in a rush to sell parts.