This is only my pers. opinion, some may disagree with me.
If it is not cold where you live, then they can go out at 4 weeks when they are done with the medicated feed (if you use that) Mine go into a separate area where everyone can see each other but not get to each other until they are 12 weeks old. Even at such a long acclimation, when you let them come together they will have to go through the pecking order of the flock and will get picked on a bit for a few days. If it gets colder than 45 no matter how old they are, I wont put new ones out there without a heat lamp in their area.
As far as feed goes. You can put them all on non medicated chick feed and offer oyster shell free choice in another feeder. Look for a 18%-20% non medicated chick starter. This is fine for adult laying birds (better than layer in my opinion), better for roosters than layer, and your chicks will thrive on it.
It is very difficult to integrate new birds if you dont have a divided area in the coop where you can acclimate young birds slowly.
I feed medicated until 4 weeks
non medicated chick feed 5 weeks to until I see an egg
then i either continue non medicated chick starter with oyster shell free choice,or feed flock raiser, blue seal breeder pellet, or a mixture of any of those with oyster shell free choice. I think layer has too much calcium (especially for roosters) and the hens that need more will take it free choice out of another feeder.