Wow man, a pretty ambitious post you've got here... No one is going to answer all the questions, and everyone's going to urge you to search. Welcome to the board I'm not stoned yet, let me give this a shot...

Eclipse GS, I don't see that as having too much potential. If you want low 12s, you better be thinking a turbo DSM. Eclipse GST is FWD and weighs less than the GSX that's all-wheel drive.

Is there any reason why you are thinking 94/95 GSR as opposed to a newer one? The GSR weighs less than an Eclipse, and the GSR motor (B18C1) has a LOT of potential. You're on a Honda-Acura forum, so don't expect too many people to be rooting for the Mitsu, especially a GS.

For parts, Honda-Acura.net has a lot of good sponsors, click the banners. There's also a For Sale/Trade forum to buy things from other users (also a feedback forum for purchases). No one company makes the best parts, it's a matter of what part you're looking at, and for what application.

I'd suggest using the search button and look for parts you're interested in being talked about on the forums, chances are, they all have been by now

Lastly, don't be afraid to ask questions, we're all here to learn and have a good time.