I have chicks coming in on the 17th. Six Barred Rock and 6 Black Sexlink - all female. I know that I need to get medicated chick starter, but how long do they need this? Do I have to switch to grower feed at some point or can I offer them the starter and go straight to layer? Also, the feed store is about 45 minutes away, so I'd like to buy enough of what I need for starter. I can get a 50lb bag for $13, how long will this last for 12 chicks. Also, do I need to give them oyster shells too? Thanks, Katrina