I am going to change the rotors and brake pads in the front only and I am not sure if I should go to a mechanic that specializes in BMW or just a regular brake shop. Do regular shops know about replacing the sensor, etc...

Replacing pads & rotors is a pretty simple procedure. The only thing that isn't obvious is knowing how the parking brake is supposed to be adjusted, which is required when the rears are changed. So you can use most any shop for this job. The good BMW shops will usually do an general inspection of any car they work on, which is something that your average mechanic doesn't have the knowledge for.

http://bimmerforums.com/forum/showthread.php?t=529851
Refer to this thread. :D

might be a dumb question, but how exactly do you adjust the handbrake?