Four pages and a week and this is what you guys tell the OP? I'm thinking maybe Bimmerforums is the place for me after all.
One of you came close with that inappropriate 'maintain before 20s' comment, but that's way besides the point.
OP, the higher you go, the more acceleration you'll loose...substantially so...and then you'll want to SC the car, cut crap off like cats, muffler, ccv, and SAP...then it's the seats, the wife, the kids.
It doesn't have to be that way. Go wide; you don't need to lift, pull, bat, or roll...just go wide.
I don't have a picture of my current set up, but in the front, I'm 16x14 and in the rear 16 x 20...that's right...x 20" wide. My tires protrude about 10" outside of the wheel arches, but I have plenty of clearance, I can go over speedbumps and carry people in the back.
I haven't had to do anything beside just the wheels. I'm surprised you hadn't thought about that too. You have to have seen my car here already, haven't you? I kinda thought that 20 wide in back was sort of a legend here. Oh well.