Not a good idea to keep a betta with guppies and swordtails, I'm afraid. Even if you haven't noticed anything yet, betta fish are easily stressed by these active livebearers, not to mention a guppy's flashy tail can remind the betta of other betta fish which can lead to aggression. Both of these livebearer species would appreciate harder water than the betta, and at cooler temperatures as well.
If you have gravel substrate, switch to sand before getting any more corydoras. You'll need at least six to eight of the same species to see this specie at its best. Smaller cory like the pygmy or hastatus or habrosus should be in larger groups. Take care that the cory you have can tolerate the high temperatures the betta fish will require. You should take a look at water hardness levels and temperature compatibility as well. You'll see some issues there further down the road. May be best to invest in a second tank to have a soft, acidic tank and a hard, alkaline tank or to choose the fish best suited for your source water (I'm assuming tap water). It's easier to choose stock for your water than manipulate your water for your stock.
