If the "catfish" is the one in your signature photo, I hope you have a 5-foot tank and 5+ more of the same type... That looks like a Synodontis decora, possibly a hybrid variation but hard to tell, which will reach ~30cm and are highly social for a Synodontis.
Until you tell us what the "gourami", "danio" and "catfish" are, the minimum temp I would go for is 22/23C. But as said above, if we are talking about Zebra/Leopard Danios then they need a temperate tank, which will be too cold for the others at 18-20C for most of the year.