Welcome to BYC. Glad you decided to join our flock. If you plan on keeping a rooster for breeding, you will need 10 (9 pullets and 1 cockerel). The recommended ratio of roosters to hens is 1 rooster for every 10 hens. As they mature, too many roosters will become very hard physically on the hens; over-breeding them, biting and plucking the feathers from their necks and backs, battering them, and potentially, seriously injuring them. Hopefully you ordered "pullets" rather than "straight run" or you will end up with a lot of cockerels. Even with a pullet order, you are likely to get 1 rooster as most hatcheries only guarantee 90% on sexed orders. If you are not keeping a rooster, then keeping only 5 pullets will work just fine. Please feel free to ask any questions you may have. We are here to help in any way we can. Good luck in getting your flock.