Rosys barbs are major pigs when it comes to eating. When i had 4, they would scarve all the food(but i did get mine to hand feed). Make sure all your fish can get food. They're also very fast swimmers and are quite active. They can be nippy towards eachother and probably even worse on their own so i would definitely get more than 3 to prevent aggression. They grow to about 2.5 inches so nothing smaller than 20gallon. I dunno, they may pick on the shrimp, not sure.
