Oh yeah, I mean to add that livebearers have to be the easiest to breed because you can buy them already pregnant if you know what to look for. Swordtails, plattys, and guppies all get the typical black spot when pregnant (the fry's eyes being visible through the mothers abdomen). Molly's do not get a dark spot but you can tell which ones are pregnant by how fat their stomachs are. There is a "fat belly" molly strain and I have no idea how to tell which are pregnant. I do not mess with them because of it.
If you are looking for nice looking fish until feeding time, consider the Pineapple Swordtails. They are my favorite of all livebearers and can often be found already pregnant.
For repeat pregnancies, I have found molly's are the horniest and waste no time in mating again. Although most livebearers will store unused sperm and self fertilize if another male is not available.