CO is a legitimate concern. An auto shut off is a good thing but how much do you trust will work perfectly 100% of the time? Do you still trust it when one failure could be your last?
My personal choice is that running heaters overnight is not a good plan. Firing it up in the morning to warm up and have breakfast, well that can be downright decadent
I’ve done some winter camping as well. Getting insulated from the ground is very key. Never used a cot but seems like a good idea. You’ll still need insulation between your cot and sleeping bag. Check out Ridgerests, they insulate great and aren’t hard on the wallet book. When I summer camp it’s one pad, for winter I learned the hard way that two is better. 1 full length and 1 3/4.
Good bag, pads, long underwear, and out of the wind you can do quite a bit comfortably. You’ll have some success and learn a few lessons too. I’ll give you a free one. Every thing takes longer in the cold. Every take 45 minutes to get your boots on? Lesson, don’t wait to waterproof your leather boots. The leather and the shoe laces froze overnight and I didn’t have a heater.
Good luck!