Print with a non-warping PLA to make sure that the disc will not get bent. PLA doesn't handle sunlight well, but neither does CDs so just keep them in an dark enclosed space free from dirt. Use only 40% infill at a slow printing speed to save plastic. 50% infill would look better, but most of the surface is covered anyway. No need for treating the surface, just cut a piece of cardboard with scissor and scalpel to make a soft bottom for the first disc.