Welcome to the M42 club!
You're avatar is really disturbing.
Anyhoo, I don't want to put you down, but you should have bought a 5 speed. The Automatic 318's are dogs. I have a 5 speed 318 and when it was stock I could barely stand it. After moderate engine modifications the car is sufficient, I'm happy. I'd never be even close to satisfied with the automatic version.
Since you're asking for ways to increase power, I'm afraid you're kind of stuck on that. Pretty much your only solutions are..
- Supercharger (DASC Eaton blower)
- Turbocharger (mossleman Garret Turbo)
- Manual tranny swap
- Engine swap (to an M3, even auto 325's are slow, no offense to anyone who has one)
There's nothing wrong with driving an automatic if you don't care about performance. However, you're asking performance, should have gone with the 5 speed. That's about the top of list as far as anything that will make your car faster.
I see in your sig that you plan on getting 18" wheels!? Well, you better make sure you like all show no go, because that's going to slow your car down even more!