Lots of good advice so far. Some random thoughts.

Take sleeping bag temperature ratings with a pound of salt. If it says 20?F, it will keep you warm to freezing for a male and 45?F for a female. Layering bags works if they don't compress one another (as noted previously). But starting with a 0?F bag that has room for warm clothing is better; this is much bigger inside than normal. For hunting/car camping, synthetic insulation makes more sense than down because it's cheaper, weight/bulk don't matter, more forgiving of condensation build up within the insulation over several days. Brands like North Face, Marmot, Mtn Hardwear, etc will cost more but are better values in the long run IMHO. Wiggy has a following but also makes a lot of bogus claims; nothing special but decent value. Never store sleeping bags compressed in a stuff sack if you want it to last.

It's hard to have too much foam insulation underneath you. A minimum R-value of 5 is essential for sleeping on snow, frozen ground, or a cot. You can stack pads to get there but putting an air mattress on top negates much of the value due to air circulation as you move.

A winter tent has a fly that goes all the way to the ground. The difference in warmth versus a partial fly on summer tents is dramatic. It also helps reduce condensation on the walls. But ones that can hold up to a snow load aren't cheap--you reeealy don't want to have tent collapse in a storm. A camper is probably your better investment. Be hyper careful about ventilation when using stove or heater inside a tent or camper. Carbon monoxide is deadly.

Much easier to keep warm than trying to warm up after you've gotten cold. Add layers before you get chilled. It's a myth that you lose more heat through your head but you still want to protect your head, ears, and neck. If you don't have a beard, a face mask can help when the wind and temps are brutal.

Stay hydrated and eat plenty of fat, all day and especially before bed--there are no bad calories in winter conditions. Be prepared for your water jug to freeze if you're out for several days. Even 15 gallons can turn to a block (burying it in snow can help if the air temp is below 0F). If you have to melt snow, make sure there is water in the pot before adding or you will "burn water". A big pot, hot stove that won't tip over, and shovel really helps.

When it's really cold, fill a water bottle with hot water and put in the foot of your sleeping bag. Just make damned sure the lid is on tight. A wide-mouth pee bottle is your friend (ladies use the funnel thingy). But make sure it's a different shape than your water bottle so there's no confusion in the dark!