Welcome to the forum and the possibility of some new darts!

Dart frogs are a great species to own and their are lots of options to choose from .

It is easiest to choose your species first and then plan a tank around their needs. Many Tinc's and larger dart frogs need a good amount of land space. Many enjoy climbing also. Most thumbnail dart species love to climb. Mixing species is frowned upon. It often leads to territorial issues and stress for the frogs, which can lead to illness. Keeping same species together makes for happy frogs .

Would you prefer a more terrestrial-type vivarium or more arboreal set-up, or both?

You may find that a more active and less shy species will be more enjoyable for you.

Here is a nice article by joshsfrogs. It sounds as if you've already done some research .
http://www.joshsfrogs.com/catalog/bl...nt-dart-frogs/

Dendrobates auratus:
http://www.joshsfrogs.com/catalog/bl...bates-auratus/

Dendrobates tinctorius:
http://www.joshsfrogs.com/catalog/bl...es-tinctorius/

Dendrobates leucomelas:http://www.joshsfrogs.com/frogs-for-...eucomelas.html

All 3 choices are great .