Ceiling height is irrelevant; your point of reference is the floor. This might be helpful:

They will be about 35.5" including granite.

The diagram Sammy posted is a good guide for the height. You could wire for your lights even before you decide which mirror(s) to buy.

We did a 6” backsplash and started our beveled, unframed mirrors immediately on top of the splash rather than leaving a space there because the mirrors were filling the whole space wall-to-wall.