I would say a sorority is a more stressful living environment than a tank in which a female betta is the only occupant. In a sorority there is competition for food and territory, and the constant proximity of equally territorial and sometimes aggressive females.
However, you can minimize the level of stress by introducing enough females that aggression is dispersed and the weaker fish aren't being constantly picked on. Providing plenty of cover and obstructions, not only discourages chasing, but also gives the weaker females somewhere to retreat to.
Choosing very young females means that there tends to be less initial aggression and territorial behaviour shown. Mature females are usually the ones that react with extreme aggression or have to be removed from the sorority either temporarily or permanently.
You want to maintain pristine water conditions and ensure that each female is as equally fat and healthy as the next. A sick fish and poor water quality can quickly cripple a sorority so you have to keep on top of these things. Also, quarantine anything that comes into the sorority for at least two weeks prior whether it be plants or livestock. You do not want to be introducing possible diseases into your sorority as this can mean disaster.