You do have a tight powder room with an awkward ceiling line. I’m glad you’re thinking about cross illumination at the mirror. I would put the sconces on a dimmer and select fixtures that have frosted glass or a shade so that they are not too glaring. You could also consider a mirror that has illumination built in so that the sconces don’t project out into the limited space. A sconce I would have you look at is the 5040 by George Kovacs. Also, take a look at Edge Lighting for illuminated mirror options.
Since you’re doing a wall-mounted sink, which I think is a good idea, I would recommend doing a little bit of “toe kick” below the sink to throw a glow of light onto the floor. I would use a waterproof linear LED tape for the toe kick lighting in the 2400K range with a CRI of 90 or higher.