Two would be all I would add.
I raised a group of nine in 56 gal column tank with Lemon tetras and a bristlenose.
Performed twice weekly fifty percent water changes to compensate for for the three or four feeding's a day for the young fish which quickly grew to adult size in under a year.
A pair formed and I gave the other's to my sister who still has them in 75 gal tank.
The Pair never produced fry and eventually they began to fight ,so I traded them for store credit to purchase other fishes that interested me.
five would work but you may wind up with a breeding pair and other's may need to be removed depending on the levels of aggression from the pair.
Or could be that no pair forms, and they all get along like ticks on a dog.