Chip would be a decent upgrade. You aren't going to get a huge increase unless you do something drastic and expensive, like M3 cams or a supercharger. A lower final drive ratio will give you better acceleration.
As for rims, I like 16s on the 325. The tires are cheaper and the ride is not as compromised. You can find a lot of 16s and tons of 225/50/16 rubber. If you go 17s, I suggest M3 wheels, as they are strong and relatively cheap used. Other than that, Mille Miglia makes decent and inexpensive rims for the 3er, OZs and SSRs are nice, but cost a little more.