The straight pipe idea could work, but adding a muffler will help with the noise, and deter cops.
Definetly a bigger turbo and a Giles Pump, I think Smokeydub's car is rockin now with that pump and new injectors, because he's running a Duramax Turbo :twisted:
Intercooler is great, I noticed a huge difference on the same crazy diesel above with an intercooler, I believe anywhere from 8 - 15 degrees, and you can even cool it further by spraying the cooler.
As for the clutch, not sure what you could use for a 1.9, I'm starting to build up a 1.6 T motor, and will be getting the 16 V pressure plate, 210 mm flywheel(lightened/balanced), and 6 puck clutch...
Bushings for you shifter, unless it's cable driven then I think your fine.
Fresh rebuild or a ring and bearing refresh....
Search the forms, and your find alot, ask a question and everyone is more than happy to answer them...