I had the same problem with my 3ft tank. Originally, I was going to divide it into four for my males, and incorporate some kind of bank with reeds, ferns and other emersed plants. Then I was thinking of a sorority, but the possibility of having to provide separate housing if it didn't work out wasn't feasible for me. So now I've decided to get a group of wild bettas (probably uberis) and make it a biotope with lots of driftwood snares, fallen leaf litter, dark, murky water etc.
With sororities there's always the possibility the females won't get along and you'll have to separate some or all of them into their own individual tanks. The only one you'd have to separate out in a community tank would be the halfmoon male. Therefore, I guess it depends on how much room you have available if you do need to set up further tanks, and how willing you are to get through the initial bumps and scrapes of a sorority.
Personally, a paludarium based biotope with the halfmoon male and some shrimp would look really nice. You'd probably just need to get a lid cut to keep in the humidity if you were growing plants emersed.