I just picked up an M-Tech Front Lip to change the look of the bumper. I'm going to paint it this weekend and install it. I'll take some pics and post them. Tonight I pre-fitted it just to see how it looks and it looks tight!
I recommend going with 18s until you decide what suspension set-up you are going with. With my 19 Hamanns, I had to roll my rear fenders to eliminate tire rubbing. Once I had it rolled, five adults could be in my car and no rubbing what so ever. How much did you plan on lowering it? That's the main factor you'll need to consider before buying your wheels, and also what size tires too. BTW-where did you get your M5 Black kidney grills?