Pacropodus opercularis, the paradisefish as you already know, is the more common of the various 'paradise fish' commonly available. It generaly grows to about 3" but willr equire a rather large tank if kept with other fish as, despite their size, they can be rather aggressive. Males, in particular, have been known to kill their tankmates and keeping two males together is almost as risky as keeping two bettas together. Sexing them is easy ocne they are at a decent size as the male has noticeably longer fins. He will also usualy be brighter and more 'stream-lined' in appearance when compared to the deeper-bodied female. Females also appear wider when viewed from above. If you ignore their aggression, these fish are otherwise ideal aquarium occupants as they are very hardy and can even tolerate pretty low temperatures. They are not picky, don't get large and will thrive in most environments. They appreciate a planted tank (also provides more hiding places and more spaces for territories to be established). Like I said before though, they can be quite nasty so find out what sex yours are and then also post your tank's size and their tankmates.
