My experience with integrating chicks:
I usually isolate for two-three days after hatch so that the chicks are strong enough to follow their mother around and know her voice, (I've had chicks follow strange hens before, with predictable results) and then integrate. I've never had an issue with that. My flock is pretty easygoing, though. And by this point, they're used to chicks.
A note on roosters:
Most of them are pretty gentle towards chicks. If one isn't at least tolerant of chicks, there is something wrong with him (as wrong as if an adult rooster was mounting a pullet, or killing one of his own hens) and he would be immediately culled from my flock.
Hens are another matter, of course. But my chicks learn not to approach strange hens within a few hours of meeting the flock. I've never had one killed or even mildly injured.
Good luck!