At 4-5 weeks most are fully feathered and can move to an unheated area. If there is a large temperature difference between the brooder and you nightime temps let them aclimate some before making a sudden change. As for integrating the flocks 4 months is a good bet. That way they are big enough to not be easy targets for the older chickens. It's best if they can be housed side by side with the older ones for as long as possible so they can see each other without actual contact.