I have seen a couple ways of people doing it and still a little confused what is the best method. I am make a couple small things but the contours are a little complicated. I normally was using a VER gelcoat and let that tack and then lay they first layer but I want to make these without the gel coat and clear coat afterwards. I've seen people spraying a mist of resin on them to get a tack so the first layer will stick or people using a spray tack like super 77. My question if I PVA the surface of the mold then use a tack spray will that show on the surface of the part??  and if it does will I be able to clean it off so I can clear coat it. This might have been asked a ton of times but I searched a little and couldn't find a direct answer.  Also I am infusing with a VER RTM resin if that helps any

What grit depends on the coating you are spraying, it should tell you on your products TDS. Most 2k high solids clear coats will want you to sand with 600-800. Don't go too light on the sanding, you still want to prep the panel properly.