i have a brooder inside my hen house. When my chicks are two weeks old I move them from the heated brooder into the hen house brooder. It has perches, sandbox, and a light bulb. Lots more room and interest. And it is with the hens who are sleeping at night and laying during the day. (and free ranging). About 5-6 weeks old I just open the brooder door and leave it open without fanfare... one by one the chicks come out, everyone already is used to everyone, and that night they are all sleeping together in the henhouse....
Been doing it this way for three years... works great!
so my answer is, some kind of separated introduction is always a good idea when introducing any new members of the family.
And of course, some pecking and posturing is normal and expected, but not to the point of real injury!