You may not need quite that much spacer. The stock M3 18" wheel is the same 8.5 width and 29mm offset, which is 11mm different. Asi it stands, your HRE will be tucked in a bit, and you may need more spacer depending on brake clearance. 30mm spacer would give you an effective offset of +8, which would be on the low side.
I have accepted a new position at Tire Rack and am no longer in the sales department. firstname.lastname@example.org
is available to assist with M3 questions.