That being said, for the time being, I will fill, sand and clear coat the surface. I have done this in the past and had some delamination of the 2 part auto UV clear coat. Is there any special surface prep required?  Do I need to sand to a certain grit, not too fine, not too coarse?  Is there a chemical prep of the surface to aid bonding?

I think that your problem is that you used some cheap lacquer. The best finish you will get if you sand to 2000 wet and then clearcoat it with urethane lacquer as this is the best composites lacquer. Another option is to use some uv stable polyester gel coat and you should just polish it after you demould your partl it's easier and saves time because if you prepare your mould properly before you will have no sanding after.