My suggestion would be to let the fry stay in your main tank from birth. Get a fish that hunts fry. Put some hiding spots in all four corners of your tank and let nature take its course. 99% will die or get eaten which is a better chance than what they have in nature. The survivors will be bigger, stronger, smarter, and faster. Adjusting your hiding spots is key to setting a survival rate but you want to cull the weak. I have fry that grew up with an angelfish, barely any survive to a safe size but the survivors are impressive* specimens. If not for some important issues that I don't quite understand, I would get into breeding platies myself.
Sure this doesn't sound like a typical breeding program but it's a start to getting a strong genetic line. Breeding platies to sell isn't very profitable (so many people have Platy
population problems) unless you get that extra special Platy
trait that becomes desirable. If you want to do this at thirteen, start mowing lawns, babysitting kids, or begging the parents, because you will need multiple tanks and a good understanding of selective breeding.
Additionally, I was told that growing swordtails release a hormone which inhibits the growth of other swordtails. Platies and swords are closely related and mostly hybridized so it isn't a stretch if platies secrete the same hormone. A larger tank, and/or less fry will dilute this hormone.
*My surviving Platy
fry that made it to sexual maturity are ALL female and highly aggressive for livebearer standards. They always spar with each other and nip at adults (including the large angel) to steal food.