Hi, welcome and good choice on car. You don't have to have the maintiance done on the car at the BMW dealership. There are mechanics that can service BMWs. What to look for is a Mechanic that had BMW factory training. Get online and search for BMW mechanics in your area and see what people are saying. After that call around to a buncha places and ask them what experiance they have ect. ect. If you are goign to garage your car, you might want to get some jack stands and take the wheels off so you will not flat spot the tires during it's extended break until May. Also change the oil and make sure all of the fluids are good before tucking it in. Then as soon as you turn the key in the car in May, go get the oil changed again and have all the fluid levels checked again. Then watch for the next couple days for leaking, some of the seals might have dried out while it was sitting.
As far as for the mileage, really anything, like brakes and belts etc., could be ready to go depending on the previous owner. Just take it some where and have them look over the car and they'll tell you what's what. Good luck with her.