If it were stripped already with CAMS approved cage, Id put it back together with only parts I needed so its on a nice diet, nice and light.
Also maybe looking at replacing some windows with lexan?
single seat
some nice power mods, Id say 250rwkw would keep me happy - so any turbo upgrade + supporting mods.
Brake upgrade with ducting (larger rotors, braided lines, pads, could even go brake bias if you were real serious)
suspension and driveline upgrades (clutch, diff, springs, shocks, caster, camber, sway bars etc)
then light wheels (with some nice gaps for air flow) and semi slicks
If you want a bit of an idea - check out Russ's (giant's) R34 build up - sure its a GTR but you can follow similar ideas