Intercooler is reccomended if you go past stage 1
Injectors will only be needed if you get a larger turbo or e85. At that point you should have already done: down pipe, fuel pump, clutch.
If you get a larger turbo, depending on how much peak boost you'll be running, you should also be considering: ebcs, bov, intake, suspension/brake mods to keep her rubber-side down
IMHO you should spend a few days searching this site, then come back to This thread and ask some more detailed questions.