That's a good looking Shack! Maybe a bit heavy for me, but I won't have to worry about that!
From my experience overnights in my insulated 8x8, a battery operated Fan is nearly a must. My shack has no drafts, but the air will stratify way more than you think while sleeping, the floor area will be COLD and the ceiling will be a heat pocket. ( BTW... is the floor insulated?) if not.... Brrrrr!
Agree about vents, though if you install them wrong... Have you ever opened a shack to find it filled with fine powder wind driven snow??
Not fun. The smallest gap can allow the shack to fill w/ snow. Usually my jig holes in the floor allow me to vent as needed.
I run a small wood stove, as well as propane. I think Propane is GROSS, Damp, and if your tank gets VERY cold they often will not work properly. More than one heat source is the way to go, then you have back up, as we have all learned, is important.
Good god Men, DON'T sleep in a small shack w/ PROPANE running!