Form what I heard uite a while ago, Endler's Livebearers are extinct from the wild
If so, try keep them in their own tank (doen't have to be big) to ensure they do not cross breed w/ other species, such as guppy. The shape of their tail is good target for nipping tetra, serpae, black tetra (big one may even swallow small endlers). As far as feeding, these Endlers are Speedy G when it comes to food.
Whether tank is overstock or not, leave it up to owner.
Have kept numerous (they just keep on breeding, used to give away to hobbyist who can do species tank ) Endlers in 90G, Heavily planted tank w/ couple hundreds of Cardinals and other schooling or shoaling tetras, corys and ottos and siamese algae eaters to control beard algae. Turn Actinic lighting when sitting in front of tank for relaxing, bringsout the colors of Cardinals, Rummy noses and Endlers. And also noen stripes or spots or patches on Corys too!!!