Hello Crystal.. I use regular acrylic paint from craft stores. I have never used anything else. As far as sealing them, I usually do not. I have noticed that even transparent chemical do sometimes give it a shine. I agree that protecting them might be a good idea. However, I consider my works to be artistic and they are displayed all year round in a horror/art room that I have. They never go outside.
I can't remember the name of the sealer that I did use on some of my things. Maybe ask at the store what they might recommend. However, do not use too much of the sealer. It also might be a good idea to test a small area on the back of your pieces in a somewhat hidden place on the sculpture. Use a very light coat and then wait. If the result is not that shinny, then you can proceed without worry.