just get yourself some fresh springs, shock rebuild kit, figure out your power situation and that's pretty much it. if you are racing on a dirt slinging track theres no need to 'upgrade' for the sake of performance. there are parts that make things easier, such as threaded shock bodies.. but nothing that improves performance on the track.
if you are racing on something hard packed that can be a little bit of a different story - though those tips are all using std parts anyways.
hang out with a few t4 guys, you might want to get one when you see what the difference is in working on them.