Here is what I replied to a member regarding e9x fitment. I believe all the info provided is spot on.
"Here are stock wheel offsets for the M3:
The wheel sizes are
18" style 260
Front 8,5J ET:29
Rear 9,5J ET:23
19" Style 220
Front 8,5J ET:29
Rear 9,5J ET:23
Ok, I believe that the wheels will fit based on this thread.
http://www.m3post.com/forums/showthread.php?t=237959
And the offsets provided above.
Honestly, I think this set up on an E90 will be amazing because they are way more aggressive offsets than what is offered through bbs for the m3.
So, in the thread I linked it is said that you can run 15mm spacers all around with no rubbing. So, that would mean that the offset of the front wheels with a 15mm spacer would be ET14. My wheels are 19x8.5 ET15.
As for the rears the lip should poke roughly half an inch more or 12.7mm than stock. So, based on all the info I believe that these should fit your car. You may need a small roll, but I am not sure. You'll see once you mount them. There is a guy running 19x11 in the rear just for reference.
These fitments aren't insane so but they are aggressive enough that I think it will give it that key stance."