If it's for school, a pair would be great..nothing like a breeding pair of cons. I did it for my science teacher over 25 years ago..worked very well back then.
go with low stocking, like a few tetras. teachers cant do weekly water changes and other things we, as monster fish keeps, deem normal. over filter over filter overfilter.
I would go with Angel fish, I set that up for my science teacher 4 years ago and she love it ! angel fish are gentle and they will not mess up the water, the water care would be easy !