Cabby-Info.com/. It will answer any questions you have about what these cars are supposed to be like, suggested and required maintenance and upgrades, and basically all general knowledge questions you will have. I'll try to answer some of you questions though;
1 - yes, you're rockin' some BBS RAs. "BBS" should be stamped on the wheel somewhere. You can find info on them on Cabby-Info.com
2 - The autoboxes are less responsive, but maybe you could benefit from a fluid change. I know for a fact they can handle 200hp though. Common thing you can do to the 1.8 for a small power boost is a cam and exhaust. The best gains will come getting your car running at 100% (oil change, plugs, wires, cap, rotor, air filter, check for vacuum leaks, replace grounds, and tuning CIS)
3 - Yes you can convert to manual. Super simple if you have a junkyard near you.
4 - They're 4x6's, and you can put 6" rounds in there if you get the pods from later cars. (90-93 I believe?)