Congrats and welcome! I'll start with the two things you'll want to check/address on your '04. As others have said:
Crank bolt - the '04's used a different (smaller) bolt that many found to work itself loose. The dampeners on these cars are not keyed, so this could be a significant issue if not checked.
Runflat tires - the grip is terrible with stock runflats, but perhaps even worse is the ride. Switching tires is one of the best "upgrades" you can do.
As for mods, many add headers, tune, gears, etc. There's also a variety of heads/cam packages as well as forced induction applications. Really depends on how many ponies you're after and how deep your pockets are.
Doug