I think it may not be enough lighting since it is a fairly large room and you would be decreasing the amount of existing lighting if you just had the sconces. I would have additional recessed lighting installed in the ceiling on a separate switch (at least 2 or 3 recessed lights). You may want to install one over the shower/bath area as well. As far as the sconces, I was trying to work out a similar situation with my vanity. For optimal lighting, probably both sides of each mirror should be lit. However, I was having trouble placing three sconces so they looked balanced and had some symmetry. There was not enough room to install four sconces. You could place the recessed ceiling lights so that they are directly above each mirror. This should give sufficient lighting and then you could install just two sconces, one to the left of the left mirror, one to the right of the right mirror.

If you decide to install three sconces, the double sconces you have pictured might be overwhelming to the space. Either way, I do prefer the single light sconce, but that's just my humble opinion without seeing the rest of the room. Hope this helps!

I thick people use way to many down lights. I'm not a huge fan of these ever popular lights.

I prefer lamps, chandeliers and such. My wife on the other hand loves the "Pot Lights"

Try going with just the two scones but have your electrician leave a large coil in the middle of the install of wire so a third light could be added in the middle and to keep the "Down Light Police" happy bury a cable in the ceiling and mark for possible placement. It is easy to install a retro fit pot light if there is room for one and you have the joist layout recorded.

Thanks for the suggestions!