There are some other threads on the ZCP/non-ZCP rim issue. Unfortunately you can't run 17's on ZCP M3 due to the bigger front rotors. There was some talk about running spacers, but the thread was never confirmed. Better off getting the stock 18's. Try finding a used set with the snow tires included. That's what I did last year.
Getting lower profiles on the front probably won't affect the DSC. Your speedometer will be a little off though and the front end ride will be a little harsher.
Can't go wrong with any of the snow tires on the market. I've had Blizzaks, Conti's, and Dunlops and couldn't appreciate a difference between any of them. You will feel a big difference in ride quality going from the ZCP 19's to the 18's. The snows are also much softer and will feel a bit squishy, but summers are nearly undriveable on M3. I almost got stuck last week when the post Sandy winter storm came through NJ and dumped a 4 inches.