I know this probably isn't the advice you want to hear, but the 320i is a terrible engine IMO. I would test drive one locally and see if you like how it drives. If you like it, then I would do a search on this forum for 320i issues as there are plenty of discussions about this.
If you still then want to buy it - then go for it
Edit: Main thread is here
http://www.e90post.com/forums/showthread.php?t=136258