I had imagined we would lean art on the ledge going across. There will be two black sconces installed (you can see the holes for them). The ledge across is kinda odd and I guess that’s what we’re trying to solve for - to make it look more deliberate, since there is no longer a pass thru. Is there a play to hang art in FRONT of the ledge as well as some leaving? To create some dimension and kinda cover the ledge?

I have loved that bathroom for several years. I used that shape for a medallion over a range in a new construction setting but not mirror. It takes a experienced tiler to do this properly. Here is a smaller one. Stunning look but you need very level and squared surfaces and a great tile person to pull this off.

Probably a pale grey non sanded, The manufacturer will have suggestions about actual type but I would want the grout to blend in as much as possible

"ashes the contractor to remove all if this. So how the mirror tiles are installed correctly?" "I did but didn’t pay attention to this" They appear exactly how I would expect mirror tile to look. You did not do your due diligence and know what you hired him to do, not his fault. Pay him to tear it out and reinstall what you want. Unfair to expect him to do it for nothing because you did not understand what you asked him to do.