True-they will become a food item for other fish....usually its the shrimpletts that get eaten first, however, if you have plenty of cover-like java moss-this will help some...also, I keep shrimp only tanks so that I can stock my other tanks with shrimp as needed....most of the species of fish I keep are rather small and I have been able to keep pretty big colonies of RCS in the bigger tanks in fairly large numbers...in the hundreds...but my tanks are also very heavy planted....they are somewhat social, however, if you start with one berried female...soon you will have many......
Just remember-more shrimp are lost/killed by the filter-be sure and check the filter box on occasion for baby shrimp-I finds lots in my filter box....in the shrimp only tanks-I either have a sponge filter or no filter at all........
I got my start of RCS and the yellow color morph from my local aquarium club for $1.00 each-so I was able to start with a dozen or more...look up local aquarium clubs-they always have stock and plants to sell fairly cheap.....and most clubs you don't have to be a member or go to meeting...nearly all have a web-site with a for sale or trade section with local pick up so no shipping charges...google your state for aquarium clubs or look in the back of most aquarium magazines for a listing of clubs in your area....