Not a Pro. I agree with above about the tv. Above the fireplace I would put a painting over the top of that alcove. From the pictures it looks like there is a ledge, so the art can be place over the top and it will appear that it is on a wall. The other alcove I would add shelves, or a sculpture, lighted up as suggested above. Some inspiration:

don't really care for the piano in that spot. beside any temp damage, the sound is right up against the wall, and the player has her back to everyone in the room. For the sound to truly be appreciated, on an upright the top should be lifted and it should be placed in a position where the sound can travel. There must be another spot for it. At the very least, try moving it to the left side where there is more room. This way you can get it away from the direct side of the fireplace. maybe angling it. perhaps at some point you could get a mini baby grand to where it can stand alone. (since the upright usually has an unfinished back panel) if not, then do a small chest or cabinet on the other side. you can do a bookcase or open shelving Or do a nice built in bench or book case move the piano to the other side and have a built in bench on the right

We are debating between the Stuv 16 zc and the Spartherm 600ZC (our preference is Spartherm due to the lack of branded glass). Cost is comparable. The only difference we can find is furniture/combustibles. Stuv 16ZC states 31" to any furniture, Spartherm 600ZC = 48". And yet many photos show rugs, coffee tables etc. far closer than 48" We have a small space. Is this something strictly adhered to?

Look at how high you need to mount the TV. You should have an entertainment center on one side. Move the TV from over the fireplace to that area. Then you can have a large, beautiful piece of art over the fireplace for a spectacular focal point. If you do built-ins, keep them to about four or five feet high for a horizontal counterpoint with the fireplace. Something like this: