At least 9. I hear young healthy hens will produce about an egg a day. 5 dozen eggs a week is 8.5a day so round up to 9 = 9 chickens. Thats under optimal conditions though, I think in practice you might want a few more in case some of them don't lay every day for whatever reason. I don't have any chickens but my aunt does and I also want a flock so I've been looking into it.