I've spent a fair amount of time in various tents - backpacking to canvas in more than a few states. 20 degree temps and high humidity does make it feel colder but your not going to freeze to death. I normally camp 3-10 nights in TN during our Nov-Dec deer season and find it rather enjoyable. Buy good clothes, a true coldweather sleeping bag, and some kind of space heater and you'll be fine.
A trick I use across the country - 20,000 btu Camp Chef stove and a propane cylinder. In the AM or return in PM, turn on both burners on high, wait 5 minutes, it will be tee-shirt weather inside. I know about the oxygen issues for prolonged use without venting.......don't leave it run forever. I've done this at below zero a number of times. Works like a charm. The other option has been a Little Buddy heater. Most come with an oxygen sensor and will shut off if oxygen levels get low. I NEVER run a non-vented stove at night - a good sleeping bag alleviates the need.
I've never slept in an Alakanak but have slept in various other spacious nylon tents. Not a fan. They are light, roomy, but very prone to punctures, burn holes, and water leaks. I'd buy a Kodiak tent. I have 2, an 8x10 and 10x14. Compared to a true frame supported canvas outfitter tent, I find the Kodiak a bit smaller despite their stated size. 2 people max in the 8x10 and 3 in the 10x14. We tend to sleep in one and eat/hang out in the other. Canvas is where it's at for comfort.
I'd also offer: buy an Alps Escalade cot and find/buy a piece of memory foam. My cot setup is almost as comfortable as my bed at home. Plus the Alps is tall enough to store stuff under the cot.
