I'm not sure about all of your questions, but I know a good rule of thumb for the live-bearers is to have two females per male, if you can manage it, and yes, they can breed with other varieties, as the different colourings and such are just mutations. It's best to separate the female before birth, whether you put her in a separate tank or breeding box when she starts to show, (make sure it's of a suitably large size for her to be comfortable) or keep watch and separate her just before birth. (A lot harder to guess. I'd suggest moving her earlier, if possible.) The other fish will start to eat them as soon as they're born, and it saves you having to chase around the tank to try and catch them and upsetting the other fish.
If you choose to use a separate tank, make sure there's something to separate her from the fry or she'll eat them herself. A tank-sized box of plastic canvas laced together with common sewing thread, so that the mother can't get to the bottom, where the fry will instinctively swim to, works wonderfully, while still allowing water circulation, or there are commercial-made variations, as well.
Otherwise, from what I remember from when my dad used to have them, which was more than a few years back, admittedly, they're fairly similar to guppies in terms of mating and gestation.