That actually looks really neat, nice work! The painting is rad. What kind of paint did you use? In general I'd be careful what materials and chemicals you put into a vivarium, but it's been mentioned (about the foam, etc). Again though, it looks wicked!
I feel obligated to mention my opinion on inhabitants, and this is not meant to be rude at all...you should always select an inhabitant first (after doing lots of research), and then build the enclosure to meet its needs. It's rarely a good idea to build an enclosure and then try to fit something in. Those are my guidelines anyway, I'm sure some people will disagree, but I feel we are responsible for the animal's best interests, regardless of what we really want.
I wouldn't put firebelly newts in there...probably not large enough space IMO...also don't forget that firebelly newts require cool temperatures, usually no warmer than about 68'ish year round. I don't mean to be a party pooper or anything though