hmmm... that would produce a wide strand of offspring comparing to just one male and multiple females. if you want to concentrate the strain, just have one male.
i breed mine in those large styrofoam boxes used to transport frozen fish and seafood, a lot cheaper than having a fish tank heheh. the downside is you won't see the side view of your fish, but then again, just for breeding. i also place plants for the reason that a lot of the guys have said here, the fry can use them as hiding places, so i'm producing plants and guppies at the same time.