All 2011 Mustangs have limited slip differential and traction control (stability control) and anti-lock brakes.
Really doesn't matter what gear ratio you pick for the differential as those things above will take care of you in the snow and ice. If you don't already have the car, I'd order the 3.73 gears to have the best acceleration in summer driving. On rare occasions in the winter when low gear is too low, I might start from a standstill in 2nd gear.
Suggest you purchase 4 new snow tires of the best proven current brand you can find...then the car will actually be fun in the winter.
My biggest problem in the winter with a Mustang was getting the defroster to defrost the upper left corner of the W/S..and I don't think they've bettered that on the new model...idiots that they are...My God, the thing was Designed in Detroit..a winter helland.
Don't worry about storing the car for the winter. If you actually live in Detroit, you are near the factory...you can just drive over to Flat Rock and pick up a new car whenever your car begins to get a little rusty. LOL.