Just a word of caution: RCS will die if the tank is not cycled and mature. For more assurance of positive results, wait until the aquarium has been cycled a couple of months. Even the lowest amount of ammonia or nitrites will kill shrimp while the Betta won't even notice.
I learned the above the hard (and expensive) way.
BTW, you can get 20+ RCS for $24.00 and free shipping from ShrimpCentral.com. Matt's the only person from whom I buy shrimp. Tried others but his have been the healthiest and very dark red. And I like the shrimp towers; although my Thai Micro Crabs evicted the shrimp.