Geoff- b/4 you start thinking of reaching 300HP(which I assume you plan on doing to a 855 R or T5), be prepared to beef-up your handling and stopping ability. Get mintex or kevlar metalic pads(for starters). Of course, bils or Konis and a tower brace are in order. The stock springs are plenty stiff, but is you want to be lower, get aft. mkt sport springs(Eibach or TMEs).
Now for your regular TU, I would suggest: Bosch-plugs, wires, cap& rotors, fuel filter; air filter(K&N), flush cooling system with OEM coolant, a good fuel system cleaner(Chevron or STP) and a tranny flush. Course, these can be done over a few months; then u can tackle the hardware upgrades mentioned above, then you can do the ECU & Exos and you are set to run with an M3 or GS400( if you can launch and handle the power). Oh, and don't forget the best tires you can afford to keep you from slipping and slidding. Good luck, BD