Re: New to vivs
12x12x18 is small for the larger dart frogs, although it should be fine for a pair of Ranitomeya. These thumbnail frogs are much smaller and faster than many of the larger, easier dart frogs so I suggest you try to go see some in person to get an idea of how small they are, because they are tiny for people who have never seen them! It also means you will need to make sure there are absolutely no tiny gaps in the tank because thumbnail frogs can fit through the tiniest of spaces.
The Ranitomeya species, for the most part, utilize height a lot, which is why many people keep them in vertically oriented tanks, but also still use ground space.
I would honestly skip a water feature completely, there is no need because most dart frogs, like Ranitomeya, would probably not even use it and it will waste vaulable space in a small tank to begin with. They are more of a pain than they are worth in small tanks in my opinion.
Not sure where you heard that you need to tear down the tank ever few months, but that's not true. A good vivarium with live plants and microfauna (springtails, isopods, etc.) will keep itself clean for the most part. You should only need to trim plants if they grow too big every few months, not tear it down at all.
Hope that helps.
azureus, leucs, green/ bronze auratus, Costa Rican auratus, Iquitos red-orange vents, mancreek pumilio, Toboga Island auratus