If you look closely at the picture I posted earlier, you may be able to see that the black acrylic has a satin finish. Easily accomplished with some fine-grit sandpaper. In my case, I had no choice since I “pushed” the painting a little harder than I should have (meaning, too wet) and some paint crept under the mask in a few spots, so I had to sand down the face to get rid of that overspill. The depth of the etch is on the order of a few millimeters. There’s no way you’d be able to sand that deep with a sanding block by hand. So you can do whatever you want to the face of the panel without fear of doing any harm to the inset lettering or other markings.
You can definitely stack materials. On these trophies, I used red acrylic and wood. The 3D effect looks better in real life than in the picture. I was pretty happy with how it came out. Of course the gear spins freely. I had to make 6 of these, 1st, 2nd, 3rd place Men’s and Women’s.