Actually 32F without wind is no big deal if you have a decent sleeping bag. Plus it gets warmer as you do more stuff inside (e.g., cooking). Igloos have the same design and can get pretty warm. [0] The real problem in my experience is that it's quite humid. Since you are insulating with snow it evaporates and raises the humidity up to the dew point.
I guess it varies from individual to individual. I can be out in 110F weather all day comfortably if I have enough water and a large hat but have very low tolerance for the cold.
Inside the sleeping bag, it will definitely be quite warm!
Even quite mediocre sleeping bags (by modern standards) are positively toasty at 32 degrees. It was common in my group for people to sleep in their underwear in the caves! Our sleeping bags were 0 degree rated, though.
Further: the major source of heat loss in a sleeping bag isn't to the air, it's to the ground. Which is why backpackers carry sleeping mats, either of expanded polystyrene or self-inflating air-mattresses. In both cases, the air is the insulating element.
In primitive conditions, pine boughs or fur skins would be used.
Other than that, wear a cap, and if it's truly cold, boil water, pour it into a Nalgene (or similar) bottle, and slip that into a sock. It'll keep you toasty (often too warm) all night.
You have to poke holes in the ceiling, and make sure the they’re clear every day.
If you light a candle, the snow will melt and freeze into a film of ice.
The holes are important for ventilation in general, but it also allows vapor to escape.
When we built them we’d use ski poles to make the holes. You don’t want them to be too big or you risk the structural integrity of course. There was a ratio of hole count : people that we followed but I can’t remember that detail (:
