I would leave enough room so that when I turned on the faucet I was not at risk of splashing my hands onto the mirror. If the mirror is on a medicine cabinet, be sure the mirror, when opened, clears the faucet handle when "on" If neither one of these issues are pertinent, then I would be sure that there is room above the counter so the bottom edge is not exposed to water. We had a mounted wall to wall mirror above the vanity and it rested on the 4" backsplash. Over a few years the mirror delaminated near the faucet/sink wet area. The mirror would get wet and run down into the bottom space between the mirror and the top of the backsplash. It just got worse and worse over the years and because it was affixed to the wall, there wasn't anything to do but tolerate it until time to do a gut of the room. As far as width, that would be your personal preference. If the mirror is on a cabinet, will the door swing interfere with side lights?

i have this same issue and i been lookign for solutions but after many calls to companies no know offers this type of repairs.. Does anyone knows of a company or handy man that can repair this ?

Consider three mirrors -- one over each sink and one in the center -- or an art piece in the center. Two larger mirrors would also work -- or the tower and a single countertop. But first, I would caution you to make sure your "great deal" really works. I think you need to do more than move the drawers -- the shelf is not showing at the same height as the drawer so that has to be moved, you are going to have exposed plumbing unless you add something to the open area, regardless of what side it is on, and the top is going to have to be modified for a countertop (the wood surround for a baby is not a good fit for a wet area) -- and that's assuming that the height is good. Changing tables tend to be lower than counter heights, so I suspect they would be better suited to vessel sinks than undermount. All of the changes risk damage to the cabinet (weakening it or requiring refinishing). I'm not so sure these are going to be the bargain you want them to be. Double check everything. If they don't work, it would be better to discover that before you start changing them so you can still resell them and recoup what you spent.

I picked out some 100 year old reclaimed black walnut and used it to frame an old mirror (that I cut down to that size) . Much cheaper than going to buy one. in fact, if you look online, you can find people who want to throw away or sell those large older vanity mirrors. They are huge. 6X5 sometimes. Take it to a glass shop and have it cut to size. then take it to a carpenter w/the type of wood you like. the boards I picked out were in 6' lengths I think. the thing weighs a ton too. The french doors you see are red oak. I got them raw. this is some of the items used to stain. the photo below is just w/the aniline dye. IAfter dying, I recommend GF gel stain in the black, then the penofin in the black.