What type of climate are you building in? That ad states how warm it would be with a heavy snow load, but in my experience, 2×4 construction will not hold up to heavy snow. Summer of 2018 was spent reinforcing my porch with 4×6 pressure treated posts every 10 feet. This area gets over 200 inches of snow a year and the builder used non-pressure treated 2x4s glued together for the posts with no footers underneath. It’s a flat out miracle that the porch didn’t collapse in previous years, taking the main house’s trusses with it. They’re tied together, you know. I’m very concerned that that structure, as is, will collapse on you. If you build it as described, please, at least put poles- I mean small round logs – in the center to hold the load.
Common issues are sizing a wood stove to the size of the living space, as running out of oxygen seems to shorten one’s life span. Any unvented propane heater will produce 1 quart of water per hour, according to my propane furnace installer. Where will the firewood be stored, and remember that firewood has to dry, or season, and that’s another source of humidity.
There’s also cob building, sandbag or earthbag construction, and cordwood building. (cordwood is firewood stacked for walls.) If you want something stealthy where you aren’t hauling in a load of dimensional lumber, they might be worth looking into. I’ve been to two cob building events. They were great fun, but very heavy work and you have to know how you need your living space to be, as it’s very hard to remodel cob. It requires sand, clay and straw.
Sawdust as an insulator: I did a test in my greenhouse on overwintering some perennials. I had planted them into a large black pond filled with dirt, surrounded by a raised bed structure so that the pond was flush with the top of the raised bed. I bought a thermometer kit with a main thermometer and 4 sending units. I laid the sending units in various locations of the bed, on top of the soil, and covered them with 7 inches of cedar sawdust. I monitored the readings all winter. The short answer is that 7 inches of cedar sawdust will keep the surface of the planting bed at 32 degrees, even when it is -40F below zero. So, if you can acquire sandbags and sawdust, or even do a fake wall stuffed with sawdust, it will make a very good insulation. It needs to stay fluffy, not packed down. I would recommend using cedar if you can, as nothing seems to want to grow in it. A rough lumber wall covering with sawdust behind it may help with moisture issues.
I also see that they have located the fireplace at the end wall. Expansion and contraction from heating and cooling will cause the meeting surface between the stones and the wood to separate and eventually rot. You’ll also lose a lot of heat through the rocks to the outside. I have my wood stove centrally located. Very happy with it that way. It’s in the basement, along with firewood storage. Heat rises, this is the most economical way to heat without having to have duct-work and fans that require electricity to circulate the air.
You might want to dig and see how far down the water table is. My well is 70 feet down, but there’s a sandstone shelf just under the soil that has water moving across it like an underground river. The sump-pump area in my basement shows the ground water is about 3 feet below the basement floor. I’ve had to paint the floor with Drylok paint in an attempt to waterseal it.
Hope this helps.