Good questions. While I'm sure that there may be some expertise here on this forum for your questions regarding conditioning cars for extreme cold climates, we are fortunate to have some very competent BMW dealerships in the D.C. area and I would check-off with one of them just to be safe/sure.
Currently: 2015 Porsche 911 GTS and 2016 Cayenne S eHybrid
Past BMWs: `05 645CiC; `07 650i; `08 M6 convertible; '08 135i; `11 750ix MSport; `15 M235i convertible
Others: '11 Panamera 4S; '13 Boxster S; '13 911 C4
"You think that's air you're breathing now?"