As for looking lived in, I checked out out some of his other stuff, and it's a young couple who look to be into a semi-minimalist lifestyle, so other than the toys in the shop, they probably don't have much in the house by choice.
I've used walk-in showers before, and built right, there's no worry about splash. In fact I would love to have one. In this part of Idaho, everyone loves their big jacuzzi tubs, and that's what my master bath came with, and then it has a totally too small shower stall, and I mostly take showers. I've thought of some day ripping out the tub and putting a walk-in shower in its place, and then putting a small tub where the current shower stall is.
On the heating, most of Idaho is either heat pump or dual heat pump/furnace systems. The propane tank doesn't look big enough for gas only in our climate. I'm sure they're on grid electric.
I thought the gun safe was too small as well, especially for a custom built-in like that. But again, young kid, and he might just have guns, but not be into guns.
Tall shop doors are a must for a rural place. I need 9' clearance just for my little tractor if I want to bring it into the shop to work on it without having to drop the ROPS.
One minor thing I would change is moving that outside planter. A planter that close to the house/foundation is not a great idea.