I think a mesh isolation box is a must. I'm still adjusting my sorority. All the females need to be the same size or as close as possible. You dont particularly get all the females at the same time but if you don't you'll have to re introduce all of them into the tank again when all the females are eventually purchased. You want at least a hiding place for every two fish in the tank plus plants. Betta fins are sinsative so either get very dlsoft and delicate fale plantz or real plants ( we all love real plants because they are sooo benefitial to the tank) if you have a regular filter youll have to adjust it to slow the flow or get a sponge filter for em. A 40 gal will be beautiful for them, you can start out with a smooth 8-10+ females. You want some of those catappa almond leaves as well. Tank mates may help, my platys tend to try to stop the females from getting too aggressive with each other, but every fish is different. Having a sorority is like introducing two strangers cats, it'll take time for them to adjust and coexist in the same tank. You always want to be home when introducing new females. Don't leave them alone for more than like a few hours (no more than 3hrs in mpo) I'm still learning as well but I hope I was a help