A big thing I would add is to strongly consider how much you'll be moving, especially when it comes to footwear.

Boots that are rated to -40 during light activity can leave you with cold toes if you're standing still in -10 for an hour.

Activity levels also dictate how you layer and how easily you need to dump heat. If you're hiking, snowshoeing, XC skiing, you want some layers with zips so you can quickly let heat out.