i have a 135gallon, 6' long.
i had purchased 7 small green chromis.
they schooled very nicely initially.
some got bigger. some got bullied. small ones got killed.
ended up with a dominant pair, and a smaller pair.
smaller pair got bullied by bigger pair and died.
remaining pair got big. just lost the male?(BIG one)to carpet surfing, guess something startled it.
though i would have liked to still have a nice school, the pair was cool, as they would hang out in the branches of my stag, just like they do in the wild.
FWIW, i believe i had read a few posts where people were able to successfully keep a handful of them together in a single tank.