I had a male Paradise and a male Bolivian Ram in a 20g tropical set-up and they got along pretty well. The paradise spent most of the time at the top and bolivian at the bottom, sometimes when they encountered eachother there would be a bit of flaring of fins, bit of aggression but nothing major. They pretty much just avoided eachother. Basically aggression is a possibility, but if you want both types of fish then give it a go.
Paradise fish are from Asia so they are a tropical fish, they are however a very hardy species and can handle lower water temperatures (suited to temperate tanks aswell).