Use whatever wood/material you would like. You can scale the images, as well, but make sure to scale them both the same.
The backing piece is one solid piece, but the top layer will need to have a gap between each piece you keep. You can see from my final image that I removed every other piece. If you start from the outer-most ring, it'll be much easier.
It looks good with or without paint, but I chose to paint this one. I painted only the top face of the top layer (so the darker, lasered edges would add some depth to it) and the top face of the bottom layer. I made the top red slightly lighter than the bottom red to help with the depth, as well.
I found it easiest to start with the outer-most ring and go inward, gluing each ring with a gap between it and the next most large ring.