I want to build some diorama as a background for my figures. I've decided on polystyrene because it's cheap and seems to be easy to work with with just an hobby knife and a blunt pencil. But I wonder what would be the best paint to use for it? While it's more work I would prefere something that's not a spraycan and non toxic so I can do it in my flat. Would normal hobby paint like citadel stuff work on that material? Also once it's dry do I need to put a top coat over it to not ruin my toys by placing them in it?