badge off asap!
you first have to look at what you have, then look at what you want to do with it.
i used this guide that helped me alot.
http://nissanskyline.6te.net/tuning_GTT.htm
if its for daily/street use, speaking from experience, keep it stockish, you dont need a daily 1mm off the ground, or something thats going to break your back. and you dont need cops hounding you, keep it quiet, keep it clean.