It is only livebearers that can have babies weeks later without a male. Tetras and cories need a male present when the eggs are laid or they won't be fertilised.
A tank of male endlers would be very suitable. Provided you don't get females they are no harder than any other fish. They are very easy to tell apart, though i would not trust a shop worker to know the difference. Male endlers come in a variety of different colours and patterns and are very pretty fish. Though to get class N endlers you would have to go to a breeder as all the endlers in shops are endler-guppy hybrids.