Here it is all painted. As you can see I changed it quite a bit, mainly by painting the background one solid color. I will mosaic starting tomorrow. I started by sanding it down, wiping it with cheesecloth to get rid of dust, and painting it with Kilz primer. Then I painted over it.
Since I also sanded down the outer edge to roughen up the surface for the tiles to stick to, I just need to prime the surface with a 50/50 water/Weldbond glue mixture before starting the mosaic. This helps prevent the wooden base from warping under the glass tiles.