I have to disagree with them being "highly aggressive" during breeding. I have a breeding pair who are consistently giving me babies and they are really not to bad. They only chase the cories away from their cave when the cories try to get in there to eat their eggs but they do not harass any other fish in the tank ( including gouramis, cories, platies, swordtails, rummies). I realize that every fish has a different personalitly/attitude but i'm just speaking from experience. I think if you give them enough room and don't cramp them in the tank they should be okay. Mine are in my 50g. and are doing fabulous.
As far as sexing them goes, its really quite easy. Males have longer fins in general (anal and dorsal fins) , are considerably more colorful and their tales are spade shaped. They also only get a light pink belly whereas the female gets a really dark pink belly. Females fins are just round and not very long and their tales are just round too. They also have more yellow on their faces then males. Heres a pic of my pair of Kribs. First one is a male and the second is a female. Notice the pink belly on the female and the not as pink and long pointed fins on the male. Normally their wouldn't be a piece missing out the males tail fins like that, his tail was nipped like that when i got him. Same with the female, her fins are kind of ragged in that picture too, she was getting beat up on in the tank she was in before I got her. Its not the best picture of her but you get the idea.
Hope this helps.
As far as sexing them goes, its really quite easy. Males have longer fins in general (anal and dorsal fins) , are considerably more colorful and their tales are spade shaped. They also only get a light pink belly whereas the female gets a really dark pink belly. Females fins are just round and not very long and their tales are just round too. They also have more yellow on their faces then males. Heres a pic of my pair of Kribs. First one is a male and the second is a female. Notice the pink belly on the female and the not as pink and long pointed fins on the male. Normally their wouldn't be a piece missing out the males tail fins like that, his tail was nipped like that when i got him. Same with the female, her fins are kind of ragged in that picture too, she was getting beat up on in the tank she was in before I got her. Its not the best picture of her but you get the idea.
Hope this helps. 
