hey man, I'm really glad you chose to check out some bimmers!
as for some of your e46 questions, I can't help you very much, I am mainly an e36 kinda guy. As for tunability however, from what I have heard, the e46 is considerably more expensive than the e36. But I can't say that for sure as I have never taken the time to research. If I were you I would get the 328, or if you really wanna be badass get the 330. Anyway, take your time, research the topics, and I hope you choose the BMW. I can promise you that it will last you a LONG time with enough TLC.