When I put on a backer I finish the top (stain or dip in 50/50 mix or shellac/alcohol).
The back I typically paint black. I like the edges to be same a front so don't paint right to the edge. If staining the front I stain the edges on the back.
I then glue front to back, I use Weldbond with good success. Dries clear and adheres well.
I then spray with Ploy or lacquer