I say that'd be nice! Idk about shrimp, but that's a nice size for the bettas anyway. As long as all the bettas are female. Some could maybe get away with a male, but I wouldn't risk it.
Edit: For stocking ratios anyway. They also DO have to get along, like John and Queen mentioned.
Of the various sororities I've run over the years the most successful ones I've found have been when you get females that are all sisters from one clutch and grew up with each other so they are already used to each other. So going to local breeders or an online breeder who can send you siblings that grew up together is your best bet. I know some people want bettas in lots of colors in a soro5and sisters are usually all the same couple colors, but it's a trade off for getting girls that are more likely to play nice.
I ran a sorority with 20 sisters in it from the same breeding for several years. I ended up with 17 females in that tank because as they grew up and matured, there were three females that just could not stop being bullied and chasing other females. They each got to go live separately as solo bettas in other tanks. Be ready to move females in case this happens. Have other tanks ready that they can go to. If you don't have the ability to do that, don't try a sorority because it is no fun watching bettas rip each other apart when you have nowhere else to put them.
Over plant the ever living daylights out of the tank. Having line of sigh breaks is super important with bettas, because if a chase breaks out, its ended when the one being chased 'leaves' wherever the aggressor was claiming by disappearing behind a plant.
I use plants which grew quick and had plenty of vertical height since bettas enjoy hanging out in the upper levels. Jungle valisneria, amazon swords, anacharis, hornwort, java fern, temple plants are all good options. I do mean lots of plants, not just on two or three. I mean you should have a hard time seeing one end of the tank from the other in a straight line. It's important to break up fights, but also gives them more to explore, which is fun to watch and they like to sit on the larger leaves. Helps keep the water cleaner too.