Take a look at this thread:
I recommend 275/30/19 in the front - but you will need to remove the camber pins and add negative camber for them to look right.
Who sold you et8 rear wheels? That offset seriously limits your tire options. I don't know what tire size will work without rubbing... I guess you could try 275/30 or 275/35. No matter what you do that wheel width / offset will look ridiculous.
KW Clubsport 3-way, Akrapovic Evolution, ESS Tune, StopTech Trophy, IND Euro Bumper & Black Mirror Covers, Turner Motorsports Studs/Lugs & Delrin Diff Bushings, MRF Solid Sub-Frame Bushings, RD Sport Sways, Recaro Profi-XL & Planted Seat Brackets, BMW Performance Carbon Fiber Interior Trim, BMW Edition Grills/Gills, Mode Carbon GT4 Splitter & GTS Wing, Advan TC3 (18x9.5/10.5), BBS E05 (18x10/11), G-Force Rivals (275/295)