What is the least number of cory cats I could put in a tank with 1 betta and 2 african dwarf frogs? I'm not sure which type I want to get yet but possibly albino.
As they are shoaling fish I've got to encourage you to get at least 6. I think 3-4 is the minimum workable number before you start being really unfair to the cats.
Depends on the size of the tank, though. Albino corys get to about 2.5-3 inches long as adults and really should be in a 24" long tank as a minimum.
If the tank substrate is the same as in your pic, I wouldn't suggest cories as their barbels will be wore off because of the rough gravel. Cories need to be on sand