if you go with the gsx, get the largest engine you can get. the more litres you have, the more torque you will have
TORQUE IS REAL POWER
for intakes, K&N, Injen, AEM make some good ones. the Injen one will run you about 200 dollars, but from what i hear its worth it. the exhaust, i would go with either greddy or thermal. they both make damn nice ones, but again it will cost you around 500 to 600+ depending on type.
fuel injectors, get some big ones if your planning on upgrading your turbo id say 625cc injectors will get you up and around
as for body kits, i wouldnt do toooo much, a different back end and some side panels, but dont put a spoiler on it. it just makes it look TOYish rather than sleek and sophisticated like an eclipse should be :sun: and get a nice paint job.
as for sound enhancements, your exhaust, intake, and turbo upgrade will more than take care of that. unless you mean speaker wise. then im not really the one to talk to. i hear one JL 12W7 sound like three JL 10W3s and have good sq.
for the turbo upgrade, get a mitsubishi turbo, a big one tho, not something puny. make sure it will push you past 300hp at least
check out
www.hahnracecraft.com
www.visracing.com
www.machv.com
www.dsmtalk.com/forums
hope that helps