I would go for one or the other on tetras, preferably the Lemons or if you can find the Von Rio Tetras, and get about 6 or 7 of them.lemon tetras-?
Amazon glass shrimp( if I can find em')
Other names for the Amazon Glass Shrimp are American freshwater glass shrimp, American freshwater ghost Shrimp, American freshwater grass shrimp. So Ghost Shrimp should be readily available.
What kind of Corydoras cats are they? If they are the albino/bronze/peppered/shwartzii(spelling?) I would only get 3 maybe 4.