To the original question, I don't, I ride year round in Minneapolis, and I've never ever worn 4 layers on my legs, My commute is more than twice as long as yours and more than likely as cold if not colder.

I really think you can simplify a LOT for length of commute. You could cut that time down dramtically. Camelback? speakers? all those layers? It's a lot of messing about. Admittedly you are really ready for anything however for such a short commute I can't se why you need to be

Hell, you could walk home in the same amount of time.

Your exhaustive description of every minute detail and process reminds me of that old Phil Hartman (RIP) character on SNL the "Anal retentive bike commuter." No offense intended.