Can you wire so the sconces will be to the sides of any headboard you get? Put them at a height that will be comfortable for reading, but at a width that will clear any headboard. If you'll get a queen or a king, just look up the widths of those two sizes and add a few inches. Styles similar to these are adjustable once mounted:

Is there a suggested height to hang sconces above a work area/desk? I'm looking at a traditional telescoping library light, something similar to the attached photo. The work area/desk will be used for sewing and crafting, so bright, direct lighting will be important.

I put bright tube sconces above each medicine cabinet because my design changed in the years between buying the lights and installing them. Originally, they were supposed to go one on either side of the two med cabs, which were going to be very close together, side-by-side. If I wore makeup, the lighting at my mirrors would not be ideal. I do believe that the designer-types here are right when they say that mirrors need side sconces. My lights project the light out into the room and do not really create shadows. But they do not really give even light on the face. Luckily, my DH says that he does not notice this for shaving! Your down lights will create shadows under every protrusion on the face - brow ridge, nose, and hair. I do love the look of these lights, but I think they are better mounted like this in a laundry or above a potting sink.

Pics, please. We have our candles to the side, and we use them, but our room is very traditional. For the holidays we used remote battery candles so we could keep them “burning” while we entertained. Without seeing your room, it is hard to answer your question.