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.
'08 E90 M3 - Alpine White - Sold
'13 E92 M3 - Silverstone II - Sold
'04 E46 M3 - Jet Black - BBS E88, KW Clubsports, Brembo BBK, SuperSprint Exhaust, Recaro
'15 i3 - Laurel Gray - Why would I mod this thing?