All the research I've done says they'll most likely leave adults alone, if there are babies around. Scarlet Badis need quite a bit of live food, so if I can get the Shrimp to form a healthy population, the Badis can have a constant supply of live food, while not having a massive impact on the adult shrimp population.
My local MA said they can get both genders in, so I'm getting them from there.
I would start with AT LEAST 10 good sized adult cherry shrimp if you are going to put them with scarlet badis. I had a great setup with scarlet badis and cherry shrimp a while back so I can verify that it is a decent nano setup. As long as you are not trying to breed the shrimp for big numbers (like to sell on the side) because the badis will eat the baby shrimp so your numbers will not grow much at all but should stay pretty steady. I never really had any issues with the badis bothering the adult cherry shrimp and truth be known I never "seen" them eat the babies but I know they did. As for the badis needing live food, I actually had some (still do) that will eat other prepared foods very readily as well as small live foods. Good luck on your source getting females as they are notoriously hard to get a hold of and most of the ones that are sold as female are males that haven't colored up yet.