Not to be a party pooper, but Paradise Gourami (or Paradisefish as it is called in my LFS) are much more like
betta males than gouramies, in other words, they really can't stand their own kind. I'd say no more than 2 in a 55 gallon hex since there isn't as much surface area for them than in a 55 gallon regular.
To differentiate between male and female, the males usually have longer fins and are darker and will flare like a betta but the females won't.
I currently have both a male Blue Paradise and a suspected male Black Paradise. I love the black to death, he is so odd even though he ate half my RCS population.