The D. auratus are indeed very nice. I would have a preference for the Kuna Yala / Chuna Yala / Kahlua / Cream or Ancon Hill or Black colormorphs.

Dendrobates Galactonotus could be nice too, as they live in all levels of the vivarium.

As for Mantellas, I think I will forget the idea as I'm thinking about building a vivarium in length, not in height, which would be preferable for them.