Don't let a stripped lock nut get you down. My tip is to get rid of those. I am like you in that I have summer wheels and winter wheels and I got rid of those lock nuts as soon as I got my car. BMW will charge you for the four new bolts but its worth it not having to worry about keeping that wheel lock key.
As for brakes, I own a 323i and asked another 323i owner about maintenance with his car and he got his brakes done at the Calgary dealership. I can't remeber how much but he thought they were reasonable. I think the important thing where ever you go is to use BMW pads and rotors.