I would cycle the tank before adding any corydoras...Some species can be very sensitive...I had my filter go out on me one night and I went through a mini cycle and I lost 2 of my corydoras...
..Also take into consideration that corydoras prefer sand bottom tanks. They are great little fish though!My second favorite actually! (bettas first
) And there are plenty of different corydoras to choose from! I have 5 corydoras with a betta in my 10 gallon..and that is 100% stocked..no room for anything else. I personally think a 10 gallon is too small for platys because they are livebearers and will quickly overpopulate a 10 gallon..unless you get all females.
I personally would stick with one schooling fish if youre going to have a betta in this tank too...More than one in that small of a tank can stress a betta out. I would stick with corydoras.