There is a definite danger of hypothermia depending upon the "type" of tent you choose to use. Eskimos live in -70F environments from one day to the next, so it is doable certainly. Native Americans as cited above have tents to provide for living in environments that commonly get to -50F (by keeping a fire burning inside the tent). A TeePee isn't what I would call portable; it's more of a temporary building (early mobile home).
But if you choose a tent that does not deal with the humidity produced by your sweat and breath, you can drench your sleeping bag AND clothing while you sleep. Moist means loss of effective insulation.
If looking for a semi-permanent place to live, learn from homeless people, or the traditional hobo. Solid walls make better wind barriers and newspapers provide excellent insulation if kept dry.
But if you want to use a backpack style tent:
Do not pitch a tent under trees. Branches falling can rip your tent.
Flooding for a backpack style tent in the winter is of no concern. So resting in a depression can block the wind.
I never started a fire; ever. I always used fuel just for cooking; really just heating food and drink.
Separate water bottles for bathing and eating.
You MUST have a closed-cell foam mat (or other non-compressible insulation like layers of pine needles) to lay on. This is NOT optional. Your weight will compress your sleeping bag. The warmth of your body will melt the ice/snow under the tent and 1) freeze you down, and 2) freeze the bottom of the tent and sleeping bag to the ground.
This is NOT subjective, this is personal experience. I used to backpack in the winter and when I first started out, I had a few things to learn. My first night it was 10F and my breath created frost on the tent inside the tent, and when the wind blew it would shake the frost down over me while I slept (snowing inside my tent). My body heat caused the frost to melt and saturated my sleeping bag (actually just very moist, not really saturated). I began to get cold and woke up groggily. It was a bit before I had the awareness of potential danger. I was only about 5 miles from home, so I got dressed quickly, even though my clothes were very moist (I was sleeping with them in by bag anticipating the morning cold). Cold, I hurriedly put everything on and started moving quickly to tear the tent down; frozen to the ground. I left it. I began running to build up my body heat. My pack was lighter because of no tent and no sleeping bag. I didn't want to start sweating, so I walked/ran to try to build body heat controllably. Was more difficult because my feet started to sweat (get cold from lack of effective insulation) before my body was warm. Once I was "comfortable" again I kept a fast pace until I got home.
Things I changed.
Good Willed my tent.
Fell in love with Gortex. Closed-cell sleeping pad. Arctic tent by Kelty (vented differently; Gortex liner lets moisture out and outer shell collects frost and slides down outside the Gortex liner). Gortex top sheet to lay over sleeping bag while sleeping (humidity out, moisture from frost stays out; a cycle of drying). Keep all my clothes hanging under the flap of my backpack at night (pull clothes in during morning to warm them up). Made lined Gortex tent bags for tent and poles, and wear these during the night for added insulation for my legs and feet (dual duty because weight is important; turn them inside out while hiking). Don't eat or drink anything within 3 hours of going to sleep. Evacuate before bed.
During the day, even at -10F (coldest I've been in), moving, eating, Sunlight, insulated foot gear, and head gear make a huge difference. But at night, none of that day gear helps.
I have almost always hiked alone. I prefer the winter because there are no insects. Sounds are softened. Water is clear. Fish are hungry. Animals are bold and visible. You can hike for weeks and not see anyone else. I stash supplies for long outings; for daily sustenance and for emergencies (keep hand drawn mylar maps of local area features and resources; cheap, and every trip it's something to do to keep the mind engaged).
Bathing is a wash cloth, and a bottle of water you slept with the previous night. Hair gets washed with the same wash cloth; no soap. Every day a water source is found, wash and wring the wash cloth out and hang it on the pack to dry while walking. Wash your feet daily also. If you are sensitive about mixing your hair and feet, then I suppose bring two wash cloths.
I keep a very small bottle of clear chlorine bleach in my pack. I put 2 drops in my bathing water bottle. This lasts for multiple outings. I use an ultraviolet sterilizer for my drinking water bottle.
You can use soap when near a water source to clean the wash cloth. But your body is at-risk for hypothermia if you drench yourself. You can clean part of your body while the rest of your body is covered. Then when warmed up again, wash the other parts.
At altitudes above 10,000 feet, do not bathe in water sources when air temperatures are below 60F. The higher altitude causes water to extract more heat from the body faster due to drier conditions and the related much greater evaporation.
I cannot address the needs of a woman, I've never backpacked with a woman. I've only backpacked in the Summer with my father during fair conditions. My summer packs have otherwise been solo except for one trip to a high mountain lake in New Mexico.