fuelpump, exhaust, fmic, turbs to 12psi will net you 190-200kw, r34 turbs might net you 200-210 on a happy dyno
3" is good enuffish for 300kw(pushing it) so unless your gonna build a beast your fine
once you do all this your pushing your engine past its stock recomendations, could blow in 10 days or 10 years, but 200kw is nothing for the 25, once you hit 250kw+ let it cross your mind
if you can, get your hands on a rb25 pfc if not you can always safc it or if you already have a tuner in mind see what he specializes in
suspension, sydneykids setup is tried and tested, see here
oh get some decent tires and make sure your brakes arnt in shit ass condition
hf