I've placed my order for day old chicks to arrive in a few weeks, complete with a rental brooder package that apparently comes with all they need for the first 6 weeks. The package description states "Package includes brooder box for a 6 week period after which time, the chicks can go into an outside coop permanently.". I have three pullets already who will be in their new bigger coop, and I planned to put the little ones in the old (small) once they were out of the brooder, but I have no idea if that's right, or if they can go straight in with the big girls? Or do they need to stay separate until they are much older? If so, how much older? Is there an ideal/preferred way to do this? It's my first time with new chicks, so I don't want to make any mistakes.