Good choice with the swordtails, they're my favorite livebearer, plus they get a bit bigger to. You can expect to have 30 fry per birth, this can be higher or lower though. They'l have babies quite often. I'm assuming you don't have a separate tank to raise the fry, so i'd try nd put some java moss in there, or something else that the fry can hide in till they get bigger.
Also, the fry should be big enough that they won't need specialy food and you can just use normal flake that you crush up really small. Also 1 male for every 2 females.