and I remember reading that they should be between 31 and 36" apart (due to space limitations ours are only 25" apart and it seems fine to me - so remember to do what looks good to you in your space despite the recommendations)

Well, we settled on mounting the center of the fixture (the round part that mounts to the wall over the electrical box) at 63", which then puts the very top of the fixture at 70" and the center of the light source at around 67". I sure hope I made the right decision. The contractor/designer's suggestion was 5" taller than the 63". That just seemed too high for me. The electrician has set the electrical boxes and the piping for the wiring, but I'm still second guessing myself. Yikes!!!

Sconces go at eye level so you may want to split the difference between your height and your husband's. You don't want to place them too far apart so that they are ineffective--36" is about the recommended distance. 36" is a huge mirror. I'd look for a 24"-30" one. Vanity, lights, and mirror are best drawn on graph paper before you buy the materials so you are sure all the elements are to scale and fit the space.

The important distance to consider is the distance between the center of the vanity to the center of one sink. That distance never changes regardless of the size of the mirror. The wider the mirror, the less distance you have between the sconce and the mirror. If my calculation is right based on the measurements you gave, that distance is 21" (please confirm it as I don't explicitly see it on the measurements you gave us). The distance between the edge of the sconce and the edge of the 24" mirror is 6.25". This number came from that calculation: 21" -2.75" (half the width of the sconce) - 12 (half the width of a 24" wide mirror) = 6.25". Now if you use a 36" mirror, the distance between the edge of the sconce to the edge of the mirror would be .25" ( 21" - 2.75 - 18"). You don't want a quarter in. wall between the sconce and the mirror. If you were to find a 28" wide mirror, that distance would be 4.25" ( 21" - 2.75 - 14"). I think the width of the sconce is more in proportion with a 24" mirror. I also think a 24" mirror looks nicer with a 27.5 wide cabinet below it.