You should be OK with your proposed tire sizes. Your front offset may require a spacer to clear your KW's but it will be close. The rear offset is pretty aggressive and limits your tire size options. It's too bad you didn't have et27 in the rear and et19 in the front. If so you would have the luxury of running 275/30 & 295/30 tires. A 295 would definitely rub in the rear with your offset.
'13 SSII M3 Coupe - KW Clubsport 3-way, Akrapovic Evolution, ESS Tune, StopTech Trophy, IND Euro Front Bumper and Gloss Black Mirror Covers, TMS Studs/Lugs, BMW Performance Carbon Fiber Spoiler/Interior Trim/Center Console, BMW Edition Grills/Gills, BMWPedals Extended DCT Paddles, Advan TC3 18x9.5 & 18x10.5 - Hankook RS3 (Track), HRE R40 - 18x10 & 18x11 - Michelin PSS (Street)