My wife and I live in our barn and here are some things that worked out well for us. We put pex in the floor and heated with an outdoor boiler for twelve plus years and a year ago switched to propane. Wood heat worked great but I went and got old enough that I didn't want to cut and split wood so much. Propane heat has not been expensive. One thing we stumbled on as important was a vapor barrier under the floor. Another was insulation around the poured slab all the way to the bottom of it as well as underneath it except in front of two garage doors. There is a huge difference in the floor temperature where the insulation was put on the outside of the slab. Should have also insulated in front of doors.
Another step that was worthwhile was 1 inch of thermatex (a hard) board insulation between the metal roof and the rafters. This kept the barn cool in the summer and no dripping/"raining" resulted from condensation- That was really important to us.
When it came time to build our house about eight years ago we checked with the assessor and determined we could afford the house but not the taxes. So a 16 ft. wide sun room on a monolithic slab was added to the side of the full length of the 64 ft.barn. Wife loves it and the deer watch us daily as if we were just fish in a bowl exhibiting very minimal concern as we move about.
As you can see they know we are there but they are OK with it.
Here is one of our long views to the east. The south is also glass(sliding doors) from floor to ceiling.
And the two ft. roof overhang keeps the snow that slides off the roof away from the house. In addition it blocks a lot of summer sun but lets in the winter sun. It is not for everyone but it fit our outdoor life style and our building budget. It gives us 3790 sq. feet for cheap and all is on one floor. Taxes are also within our budget.
We are still working on the sun room inside to have it contain a kitchen, living room, dining area, kitchen and hot tub. Dining area with a gas fireplace and living room with a second gas fireplace and the hot tub are in place. There are no interior walls planned for the sun room. Good luck in your barn build, whether you stay in or not it is likely to be one of those things that you will really enjoy.