First time raising chickens and I decided to buy mixed breeds to get duals and layers. Well all the chickens are 19 weeks old and 7 out of 20 are roosters. Well I have marans, araucanas, orpingtons and wyandottes. Some of the hens will be laying soon but the araucanas are still months away from laying. What feed should I be feeding for week 20? Should I just give them a container of oyster shells so the hens have some calcium with the grower feed? When should the araucanas be given layer? I should be fine with giving the roosters layer in a month, right?