Oh ya, it will be a peck fest if you just throw them together and the young ones will be the receivers. The look but don't touch method is recommended. And usually actual integration when they are close to the same size. I have 3 BR that were 8 weeks older when I decided to introduce my 10, 8 week old's. Even after more than a week of look but don't touch, the BR bully them, chasing them away from the feed and chasing grabbing feathers every chance they got. Now 4 weeks later thing are starting to settle down. The BR were in a small coop, I moved the littler ones in the large coop and let them settle in before adding the BR. I can tell now at 12 weeks the young ones are starting to wonder what they are running from. So I would only do it after a period of visual separation and then with supervision. Provide lots of visual interference or places for the smaller ones to hide. Really I don't recommend it, but... who knows. The #s were in favor of the younger ones in my instance and it didn't help a ton. But it can be done. Also, breed may play a small role.
I use an all flock feed because I have mixed ages and cockerels and the amount of calcium in layer feed will cause kidney issues. It is ok for you others to eat the starter, but not vice versa. I provide oyster shell on the side, only the ones who need it will use it. You can always put aside your layer feed until they are old enough, although freshness may be an issue at that point.
Best wishes!
