We have a rwd M Sport w/summer tires, so I need another set for winter - I'm going to do same thing I did for our departed [rwd] G35 - not sure if this plan is feasible/convenient for your situation, but I get a wheel & tire set from Tire Rack for about a grand, then I keep them in the garage & when time to change, I put them in truck (now GTI) and we take both cars 3 miles to local tire shop and pay them a measly $20 to do a "rotation". This is partly bcz it's convenient/bad back/lazy.
Overall I think this is pretty economical - you don't want to keep unmounting/remounting different tires on one set of rims twice a year - the cost of a second set of rims will make up for that (mounting/balancing costs) in not much time and, just as important, you will save time at tire shop by having two sets of rims.
I don't worry about TPMS while the car has its winter shoes on - I get non-RFT winter tires (I recommend Bridgestone Blizzaks) and just let the indicator light stay on for three months. Not worth the cost/trouble to fuss w/TPMS for short period.
Don't do this thru BMW dealer - not economical - they charge about $700 for ONE winter wheel/tire. You can always save the extra rims/tires for your next BMW to use, or sell them.