Leslie, I mean you no ill will. I was offering an opinion which is what your original post asked for. Please don't shoot the messenger after asking for opinions.

My concern is that for a living structure there are specific guidelines (laws) as to what is "code" in every county in the country. If you are obtaining building permits for such work that is the time to ask for guidance in what you are about to do. For a pole barn the regular studding isn't always necessary, for a living structure it is. I guess I have just never seen anyone, or any company do things in the order you are doing them in and frankly I don't know if your plans to side first, stud and insulate later are going to work out the way you're wanting them to. I hope they do for your sake as I am sure you have made quite an investment in the siding materials already. It might be worth your while to spend some money consulting with a contractor even if you want to DIY the work. A contractor will be able to give you invaluable advice and suggestions from start to finish.

This is going to be a very difficult area to heat during the fall and winter months when most hunting occurs and even in the early spring during turkey season etc. It's basically going to act like a huge funnel sucking all your heat right up to the top. I am a farmer/rancher with well over 5K acres and I own a multitude of barns, shops, outbuildings etc. so I know the difficulty in heating even a small fraction of them. You might consider adding a number of wood burning stoves (more efficient than a fireplace) in various areas of the building. Taking into consideration how rooms will flow into each other to ensure that the placement of the stoves will allow as much air to circulate as possible from room to room. My house on the ranch is a mere one bedroom with a loft, over 100 years old and as cold as the dickens even with full insulation, propane heat and a giant fire box wood burner in the basement. Consequently, we live in town during the winter for the added wind breaking abilities of the town around us. It takes a good amount more heat to heat a building on the open prairie than it does in a community with a lot of trees and buildings to buffer the wind.

As far as radiant heating goes, are you talking about the wire type that goes under the tile to keep your tootsies warm or are you talking about a radiant heat floor system to heat the structure? If you are wanting to heat the structure by placing tubing that you run a hot liquid through you're already basically too late. If your doors were not installed already (and I have no way of knowing what else) you could run all the tubing and place another layer of concrete over the existing slab. Ideally the tubing should have been placed before you poured the slab. You will need a large water heater or a broiler system to put in radiant floor heat and this should all be installed before you add another slab over the top of it. It is a great way to heat large buildings with cement floors though!

You mentioned stairs but did not say where the stairs went to, is there a second floor? Or even a partial second floor? What is there for a roof on the structure and has it been insulated? Traditional pole barns don't have attic spaces etc. so there is no place to add poured insulation, all insulation would need to be attached to each rafter before putting up the ceilings. Which brings up another question in my mind....what is the spacing of the rafters or will you need to add studs up there as well?

Is the plumbing in place? Is the electrical service installed into the building?
No intention to offend you but these three pictures leave us very little to go on with what has been done and what needs to be done still, though we all understand the dream that you have. More, CLEAR information would help us all a lot more or many more pictures of what you've got going on.

Having said all of that...if you are just in the dreaming stages of what to do with the interior when the rest of the structure has been completed then just say so, sheesh, we all love the dreaming stage as much as the finished stage. When I read the information you have posted I did not really clearly understand what it is you are wanting to discuss or get suggestions for and still don't. I honestly thought you said you wanted to keep the floors, walls, etc the way they are except for the stairs. Hope this is all helpful. If not just disregard it completely.