Seems fine I would knock a school out and have one huge school of a tetra then the school of cories. Tanks with too many schools to me look bad, there us too much in the tank. There is a guy on YouTube that has a huge tank 55 or bigger and the only fish in there are neons. It looks nice.
I plan on having a 16 gallon with a like a school of around 5 cories and 12 neons, maybe more I don't know.