For a good sorority tank I would say at least a 20 gallon long, very heavily planted or if you are using silk plants again very heavy on the plants. I would add 5 to 10 female and do it at the same time. Add them when the lights are out. The reason for what I have said is this. The pecking order in female betta is like putting cats in a bag. If added at different times there will be fights and those fights will (not might) be from dominance of one female and she will control the tank. In most cases the fights between them will result in death, of one or more.
Female betta will co-habitat as long as there is excellent cover for them to hide and get away for the others. The more females you want the bigger the tank you need.
DO NOT introduce a male betta into the sorority tank. When trying to breed remove the female you have selected to a separate tank Other than the one that you have the male housed in. Put the tanks together as close as you can so they can see each other and nature will take it's course. The male will blow a bubble nest and the female may ( not always) will show breeding bands and will be egg laden.
At this point you introduce the female into the males tank.( keep a very watchful eye on them at this time.) They will do what is called a breeding dance ( This is an amazing thing to watch.) While the dance is on going the female will release the eggs and the male will retrieve them and place them in the bubble nest ( the female may help or she may start to eat the eggs. In which case the breeding is over and the male will either chase the female away or try and kill her. Remove the female as soon as the breeding is over back to the holding tank( DO NOT put the female back into the sorority until you slowly introduce her back to that tank and only when the tank is dark.
I’m going to be frivolous, and say ‘if you are asking those questions, then you are not ready to start a sorority’ - but of course you already know that 🙂 or you wouldn’t be asking 🙂
My advice would be to read up on the many sorority articles out there, and then get a bigger tank than they say. Then plant it with huge numbers of plants, and let them grow and thicken til they fill the tank. That will take months. Plenty of time for a fish less cycle. Add many, many caves and shelters. Then add the girls all at once, while immature. And don’t add a boy.
But, in all honesty, I would not advise you to try a sorority unless you have masses of experience and already know the answers to all your questions.
Sorry to be so negative. Genuinely sorry.
But if you have a look through previous sorority threads, they rarely turn out to be successful long lasting setups. And the stress levels often lead to unhappy, nervous, ill fish 😞
The answer to housing them together from my point of view is to say no. I don't know where the information came from as to housing a male in a sorority tank came from but I have always been told by members that this would not be a good idea.