With the sport package, mine came with 17" rims with 225/45-17 Michelin Pilots. I'm going with some 18" Enkei rims and 235/40-18 Continental Extreme Contact tires (specs were just as good as all I researched but treadwear was twice as long--400 as opposed to 200 on most). Yes I know the compound is slightly harder. I'm using my OEM 17" rims with some Yokohama 225/45-17 snow tires. You may want to get tires not so wide to cut through the snow better. I'm doing the 6 months snow/6 months summer change-out.
I did look at Bimmer wheels but they weren't "unique" enough for me.
Make sure you let them know whether you do or do not have the sport package because the caliper size is different. To answer your question on the sport package 17s, the bolt pattern is 5-120. Also, you will most definitely want to get 40 (as opposed to 45) profile tires so as to not offset your overall tire/wheel profile and mess up your speedometer reading. Besides the 18s, I was also looking for fatter tires, hence the 235s as opposed to the 225s. If you really want to be pimping, get 245s.
Have fun and post pictures