Congrats, wheels look great on M3. I wanted to initially go with Vorsteiner as well but then went with Vossen VFS1 as I was waiting for ever to get the Vorsteiners.
Yes, 285 is the way to go, I would have gone wider if it were feasible. I have 245 at the front and 285 at the rear. Have you got a chance to test the range yet? I have so far managed to get 245 - 250 max.