I use a 18x10 et25 set up all around. With 3+ camber up front and 2+ in the rear.
Due to the amount of camber, I can easily use 10 mm spacers front and rear on 275/35/18 Continental scrubs. However, it is pretty tight in the rear (tire to fender) with spacers. There's plenty of room if you don't use spacers in the back.
Front space I cannot say since I have aftermarket struts.
One consideration is that there are not too many tires available in 285/35/18. 285/30/18 offers more but you would lose your side wall.
Another consideration is the balance. The M3 understeers from the factory, so depending on your set up you may prefer a square over a staggered.