I would not put anything wider than 275mm on a 9.5" wheel. A wider tire will not have good support. I would also not even consider the et35 wheel as it's too far off the correct offset for an M3. Especially considering that Volk makes their wheels with some of the best M3 offsets (no spacers required). There are plenty of used Volk wheels available on this forum. Keep your eyes on the wheel/tire for-sale section.
'13 SSII M3 Coupe - KW Clubsport 3-way (Eibach Front Spring Conversion), 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, Mode Carbon GT4 Splitter, Advan TC3 (18x9.5/10.5), BBS E05 (18x10/11), G-Force Rivals (275/35/18, 295/35/18)