Height of ceiling does not matter. Placing the lights too high will cause shadows on your face. Mirror width is important- you need to make sure hen you put the sconces up the mirror you like will fit. It will be a little more difficult to find a mirror you like if you put them too close together. The lights generally look better if they do not go outside the line of the cabinets, but there is no rule.

Bedroom, Powder Room, Bathrooms, Dining Room, Foyer, Hall,Sometimes Living Room. This is really a design decision and you need to have a furniture layout in hand to get these wired (or they will be in the wrong places pretty much guaranteed:)

I need the same replacement glass. My tenants moved out and I discovered they broke one of the scones in my 16 piece chandelier. I can find all of the lights but no replacement glass. $120 is a lot to pay for one piece of glass.

Place the single sconces the same distance from the mirror as the double sconce is. But with only 1 inch difference, nobody is going to notice either way. That being said, I think we would be friends. Good luck!