Just want to point out, sorry your paradise fish killed each other, Shirley. Lesson learned I guess, pet shop people are crazily uninformed sometimes- they see the species kept together in the same tank and assume it's fine to do this long term.
Most sources say to keep males solitary, while females can be kept in small groups since they are less aggressive.
It's important to remember that all these anabantoids are aggressive. Like I said at times they are forced to fight for resources like crazy.
I'd say in general, aggression levels are betta splendens, paradise fish, wild betta, then gourami, from most to least aggressive (there are QUITE few exceptions, such as noble gourami who are all jerks to each other). Even peaceful gourami such as honeys have been known to kill each other (male vs male), for no apparent reason. I like to assume that something small, probably undetectable, happens in the tank that kick starts their aggression, like how a dry season in the wild would turn on their aggression, but it's just a thought.
All these fish are quite close to my heart (they were the only ones that didn't die in my horrible fish tanks when I was little). ^-^
Btw, not pushing you into paradise fish, kfry, they were just the only other small solitary fish I could think of. I'm quite excited to see this flame gourami. :D