I don't know how much help I'll be, because I'm looking for the same answers. However, I've read in older posts that Polyblend is a safe grout brand to use, also that they use a mix of sanded and non sanded (to add textures, ect). People do seal after grouting, from mod podge to watered down gorilla glue and either painting it or spraying it from a cheap water bottle. If you are planning on painting over the grout definitely seal it, as it's water based and if your dragon decides to make a mess, it could be dangerous. I hope this helps a bit as I'm not an expert yet haha
The grout always has to be sealed, it's super porous and will absorb any liquid, it will also flake off if you don't seal it. Usually they even seal grout when they put it in for real floors ;P