If your $5000 is for the motor only then thats a very healthy budget. i am not too sure on which SR20de vould be the go, but if you are going to be moddifying it a lot anyway, probably start with an S13 variant as it should only cost you $500 - $1000 depending on what you want with it. DO NOT waste money on an R32 box, the SR one will be strong enough. Unlike the turbo's, there aren't easy bolt on ways to make power (above 110rwkw), head work and cams are the way to go. Ask Ferral Errol, he knows about them.

i like the sound of your project!