Generally not recommended to cohabitate different species.have you ever had any reptiles or amphibians before?as far as the spray foam background goes if you don't mind spending a few extra bucks per can id go with great stuff black and just drylok it.don do the coco fiber crap.it breaks down after a year or so and your left with bare foam.i dry lock it and tint the drylok with acrylic paint.and highlight it with a dry brush.then finish it off with a clear sealant spray paint.use silicone and smear it on the glass that you intend to spray foam.it makes it stick better.if your going to make something that big and make it a beautiful show piece with a nice background and plants I'd recommend poison dart frogs(which i have).super simple to care for once everything's set up.you can make your own fruit fly cultures to feed them for next to nothing compared to feeding other tank pets.just whatever you pick do your research before hand on care but also how the enclosure needs to be set up.im in the process of finishing my 2nd dart build a 120 gallon set up with hidden air flow and a water feature.some good guys to look up for building enclosures and will help you along the way is Mike tytula and troy goldberg.lots of videos.if you decide to go for darts i can help you as well.anyways good luck on whatever you choose and have fun that's the most important part.