We recently built a 40x60x14 iron barn with a plan for it similar to yours. Our primary usage is a weekender for the ranch. Apartment inside with upper and lower bedrooms, closets, a bathroom and a kitchen - all walls and ceilings are fully insulated with roll fiberglass. Floors are LVP or engineered wood. That takes up about 21x22. 4Ton HVAC - with a long trunk on a damper to make the barn a separate zone. 1" of spray foam insulation throughout the barn. Walk doors on 3 sides and big doors on each end - 12x12 & 12x14. Conduit-ed electrical and 200A service. A couple things we WISH we had thought of is to put in hook-ups for a washer and dryer. We are kicking ourselves for not plumbing that into the floor before we got started. Too late now without trenching the floor. Also, out kitchen runs out into the barn along the front wall in an open-style layout. If I did it again, I would have enclosed the kitchen so the AC would cool all the living spaces. It's hot as balls here already and the AC in the barn (and kitchen) really struggles. I dont want to put in a mini-split in the barn and adding more insulation is too expensive to retrofit, so it's going to be expensive during the summer. Some things we did get right...We polished the concrete floors and it really keeps down the dust. I also added brushes to the edges of the roll-up doors and they are a game-changer. There are no wasps, moths, flies, etc. that get in. If you are in a "safe" place, put in as many windows as you can afford. A walk door near each rollup is helpful too. Maybe consider making a covered porch. The porch separates the dirt from the inside and is a good place to grill, sit and relax, etc. Finally, budget about 2x what you _think_ it will cost!