Reliability: Depends heavily on previous owners. Apply this to all of your questions. I sold my modded '02 with 56k on it and it didn’t have a single problem.
Bolt-Ons: There are a lot out there, and they are significantly more expensive than the next car. Cobb’s reflash is a cheap alternative to the TurboXS UTEC, but the rest of their parts are overpriced when compared to the competition.
Engine/Clutch/Tranny: Depends on DRIVER. I had alot of “fun” on my car and was still on the stock clutch/tranny, but I launched it maybe 3 times in the 2 years I owned it. Engine will hold up fine. Tranny isn’t the best. Don’t expect it to make 300-350whp and not explode. Mike (Innovative) Tom (dozr) Nick (RedRRocket) all ate theirs. If you don’t drive like a retard, your transmission will be fine, pending your power output. If you are into auto-x or rally like those guys are, expect shortened life. It’s not glass, but it’s not going to take abuse either.
Tuning: Cobb Accessport: Reflash for more power. Works ok. You can step up to ProTuner / Street Tuner and get a more refined tune.
TurboXS UTEC: Boost/Fuel/Timing maps, launch control some other stuff, more expensive but still not detectable during inspection and allows for datalogging.
If you buy one, Intakes are bad, MBCs are bad, and atmospheric BOVs are bad, unless your car is setup and tuned for one.