sorry double post. I did not see it b4

My floating vanity ended up being only 6 inches from the floor. This was because of existing plumbing that i did not want to move. It did not look like a floating vanity. so the enhance the effect, we added lights under the vanity! so when the lights are on the effect is nice otherwise it does not look to be floating. I would say 16" will create the separation needed for a true floating look but then your vanity ends being very small for storage...You can do a mock up with some cardboard boxes.

Yes you should take into account the height of the faucets. Normally a mirror would begin above them. (Think of what you want to reflect....lots of plumbing or the viewer?) You want to be low enough that a person who is 5' tall can easily see their entire face and chest. Typically that's going to be right above the faucet. My powder room mirror is pushing the height limits at 45" above the floor. You don't want people to have to stand on their toes to see their face and chest. Mine is 4" above the faucet (so it's not crowded since mine opens). I'm sitting in a hotel right now and the mirror is right at faucet height (you don't see the faucet reflected in the mirror). I'd say it's about 38" off the floor. It's quite comfortable to use. My higher mirror is a powder room mirror as well. I did a lot of research on the subject (suprising how much you can find on the internet) and the general concensus was that you should look to the short folks in society and cater to them for the bottom height, and the tall folks for the top height, so that someone 5' tall and someone else 6'4" will both feel comfortable in the room.

My mirrors are not medicine cabinets as in the photo, but they will be recessed with a casing surround. Again, thanks for bringing this to my attention. The mirror will be recessed about 1/2-3/4" once the casing is on, I believe, so the sconce would actually extend an additional 1/2 to 3/4" out from mirror when attached to the casing. I understand why you'd recommend the shallower configuration. Thank you so much!