Do you have experience in keeping tropical fish, if so..You will need everything you would use for a regular tropical fish tank...ex. heater, filter, live plants, lighting.. etc.
But when selecting your females..look for the smaller females that all look to be the same size. The smaller the female, the younger..and having younger female bettas help them get used to having tank mates at..which lowers the rude behavior between them.. Also. Are you looking to add tank mates in with the females?