Looks better with the inner lining buttoned only imo
Also max-t, I think most of the stock for SS is out now so you're not going to be able to find a size IV from the usual SS stockists. Some places in Japan might have one though, but you'd be paying an arm and a leg plus proxy plus shipping
I'm not sure. I tried it on real quick and it was hot as fuck but I live in the bay area and its like 90 degrees right now. It looks pretty warm though as its alpaca out and lined with wool on the inside.
For extreme weather you'll probably need something else, but designer shit is never designed for like -10.