You will want to put your new froglets or juveniles into a small nursery or quarantine tank anyway before you introduce them to the large vivarium. (I use small 2 gallon fish tanks with hinged glass lids, just wet paper towels for a substrate along with some plant cuttings and a couple of hide spots for a "nursery."
Critter keepers with the vents sealed or even plastic "shoe boxes" are sometimes used as quaratine/nursery tanks. Let them grow a bit, make sure they are eating and healthy, or they may indeed get lost to your ability to monitor them in such a nice large tank. Older darts do learn quickly where the food source is concentrated, but the froglets and juveniles may not be able to find it as readily. I wouldn't mix any of the species together, at least until you get some experience. After six years, I haven't done this yet. With such a nice large tank, divisions as Dan suggests might work pretty well. Depending upon what you get, some darts are extremely territorial, so read up on the care sheets before you choose.
In any event, you have a lot of fun to look forward to.
-----
Patty
Pahsimeroi, Idaho
4 D. auratus blue
5 D. galactonotus pumpkin orange splash back
5 D. imitator
6 D. leucomelas
4 D. pumilio Bastimentos
4 D. fantasticus
4 P. terribilis
4 D. reticulatus
4 D. castaneoticus
2 D. azureus
4 P vittatus