I own a large colony of black bar endlers. Not the least bit fussy about food or water conditions. They will breed continually. They are smaller than guppies generally and pregnant females do not usually get big and bloated like guppies. I literally see new babies every day. I do not keep any other livebearers so in theory my strain of black bar endlers breeds true. Since they breed so fast, a large tank is a good idea. Mine are in a 60 gallon although I started them in a 20 long which they outgrew. They are ridiculously hard to catch. Basically scoop and hope for the best. There are always people interested in buying them so you would not have much trouble selling. I can't be bothered, though.
One word of advice - since they eat so greedily, my bottom dwelling fish don't stand a chance at the dinner table. I use the flow of my HOB to force food down to the substrate level for small cichlids or corys. Endlers are very entertaining and lively.