I second getting lots of information and first getting the fruit flies and getting that working. Darts are small and much more demanding to keep than larger species, so it's really important to have food for them all the time and keep all the other things in check. Well, Agrippa said it all already. Read up everything you can find from
www.dendroboard.com forum and website. You will find everything you need to know about dart frogs from there.
I think people usually plant the plants straight to the substrate, or mount broms and others like that to the walls, wood branches or something else.
Darts do go to the water feature occasionally, but their terrarium still needs to have high humidity for them to enjoy their surroundings. Normally they will only go to the water when depositing tads or when they want to clean themselves up. If the air is too dry or if the frogs are ill, they might spend a lot of time in the water (which is not a good sign). So it's important to keep the humidity level high enough even with a water feature in the viv.
They deposit the eggs on a plant leaf, coco hut with petri dish on the bottom or something else like this. The male will keep the eggs moist and watch over them until they hatch and then it will carry the tads on it's back to water.