Seriously, the primer soaks into the board.. you will still see all the mud joints and nail holes. But that's what it's supposed to do.
You can definitely spray it.. the stuff will soak in, no need to roll.
Good to hear from you. I was wondering how things are going.
I would think 7" would be fine. I don't have my screen up yet, but I was measuring various distances from light to screen and decided 8'-12" was a good distance.
I'm sure others will chime in who have their lights and screens up.