OK, I’m going to buck some of what is here already.
We came from the coast, warm and wet climate. Moving here, 3000 foot elevation, and semi arid, and cold winters with snow. -30C in winter is “normal” for some weeks, on and off. Have been down to nearly -40C. Old timers tell of -56C on occasion. You can do the conversion to farenheight.
We have TB horses, and crosses. I had a stallion, and youngsters, and mares in foal. We quit racing with the move, and I still play around in the h/j world.
I was thinking about the barn to build, heating it, blankets etc. Here’s what I have learned in the last 15 years.
The coldest place for a horse to be in a cold climate is IN A STALL. Do not build stalls. It is very important that a horse can move around, run around, to warm up. Put horses in a group, in a herd, and they will move. They go to the spot where the sun hits the pasture first, and wait there for the sun to show up in the morning. Coats are thick, and provide great insulation (yes, TB winter coats work great). You can tell that the insulation is good, because the snow does not melt on the horses. Blankets reduce the natural insulation by flattening the coat… they usually do not work as well as the natural coat. There may be exceptions to this, if there is a problem with the coat, or if the horse is infirm. But under most conditions, the natural winter coat works great. Heating a barn is a huge fire risk. Don’t do that.
You can provide a shed, my horses rarely use the shed, but it provides shelter for the salt block from being leached by rainfall, and keeps the auto waterer out of the sun (which helps it not build up algae). The horses rarely use it, but it’s there if they want to. The pasture has lots of trees, and the horses usually prefer to bed down under the thick cover of trees.
Feed lots of hay, more than you fed in warmer climates. Ours eat free feed hay, which is not a problem for us because we grow our own.
I do not ride in winter. Snow and ice is a reality, slipping around getting to the arena is a distinct possibility that I don’t need. Get some ice cleats for your boots. To ride in winter in very cold weather is no fun for anyone. With thick coats, horses get wet, then cold quickly, and can’t dry off. Get chilled. Clip the hair off to avoid that results in horses having to live in heated stalls, with multiple blankets etc, where they get impaction colic and hoof contraction. Don’t go there. Leave the horse alone until spring arrives. Which it sounds like you are gonna do anyway with your old guy.
This will be a tough move for your old horse. There isn’t a lot you can do about that. Be prepared to deal with that.