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.
2011 Panamera 4S...GT Silver / Espresso
2013 Porsche Boxster S; 2012 Mini CooperS
convertible; '04 GX470
Prior BMWs: `05 645CiC; `07 650i; `08 M6 convertible; '08 135i; `11 750ix MSport