330ci can fit 4 people comfortably (unless they're all 6 foot+). The room in the coupe and the sedan is practically identical. The thing is, if you're being practical, I wouldn't suggest a coupe. (One of my best friends is a sports sedan guy; has a C32. Nothing wrong going the sedan route) Particularly if you go off to college with it. Moving in a coupe is a pain in the ass, and in college, you tend to move a lot. The seat only tilts so far. I bought a bar-b-que and could barely get it in the backseat. If I had the sedan, I know it would have easily gone in. Plus, going out with friends is a little harder.
See if a used E39 5 series is in your price range. A 540i would be sweet. Your prolly wouldn't even have to supercharge it to get the performance you want (saving you the reliability concerns). Or, if you're determined to use forced induction, a 530i uses the same engine as the 330i. Prolly uses the same supercharger. Be cheaper and simpler to just go straight to the V8 tho. From the numbers I've seen, it's cheaper and easier to go up to the next engine level if possible. For example, a supercharged 325 only goes about as fast as a 330. Supercharged 330 goes about as fast as an M3. Etc.
See if a used E39 5 series is in your price range. A 540i would be sweet. Your prolly wouldn't even have to supercharge it to get the performance you want (saving you the reliability concerns). Or, if you're determined to use forced induction, a 530i uses the same engine as the 330i. Prolly uses the same supercharger. Be cheaper and simpler to just go straight to the V8 tho. From the numbers I've seen, it's cheaper and easier to go up to the next engine level if possible. For example, a supercharged 325 only goes about as fast as a 330. Supercharged 330 goes about as fast as an M3. Etc.