Yes, a sorority would definitely be possible. :) You don't want to go any smaller than a 10 gallon tank. I've done that with a 10 gallon tank and it worked rather successfully too.
My personal advice on sororities- quarantine each fish for at least a week to make sure it's not ill. I think that was my ultimate mistake.
And naturally, make sure tank's water temp is similar to each fish's water temp when you add them.
Good luck! :D