I have a 25 gallon with I think 20 something? females in there. I removed a couple (one for breeding and one who didn't like the sorority environment) and had one of my oldies die recently, but other than that everyone does fine.
If you know what you are doing and keep on top of managing aggression and water quality you could have between 15-20 odd females in there and they should do fine.
If you are less confident, want to be more conservative or have other fish in there as well, a good number would be 10 or so. Different tail types really don't matter. It's generally the females you wouldn't think that tend to be the aggressors in sororities. I have HMs, HMPKs, CTs and giants in my sorority and never had any issues because of it.