Truthfully, I wouldn't worry about any of those things. I'd look at two things.
What type of sconce is it? Does it directly radiate light through a translucent cover, or is it opaque and does it rely on projecting light up to and bouncing off the ceiling? If you mount the former higher up, it will be able to get light further into the room without causing distracting shadows from chairs and people moving around. If you mount the later higher up, you will get a concentrated "spot" of light on the ceiling right above the sconce, but probably won't get very good projection of light into the center of the room. (Not related to placement, but if your sconces rely on bouncing light off the ceiling, and you are planning a dark ceiling, you're going to need a lot of wattage to make them light up the room.)
Are any of these going to be placed in walkways, possibly along the isle to get to the back row? Are you going to be placing them such that a guest, maybe walking a little too close to the wall in a dark theater going to/from a bathroom intermission, is going to bonk their head on them?