I do not quarantine newcomers, but I DO segregate them for about a month. I didn't have enough space to keep new birds far enough away for a true quarantine (as some stuff is airborne). However, new birds get their own segregation pen with attached coop, their own feed and waterers. These pens are not big enough to be considered a "run" so the newcomers have to see other chickens ranging around them, freely. And dream of the day they aren't cramped in their segregation coop...
But it lets them see, hear, and puff up at each other through the wire pen walls. Come the day I let out the new bird(s), they are no longer strangers and the establishment of the new pecking order is seldom more than a bit of a peck, a feather pull here and there, and maybe some neck feather ruffling with a few squawks.
However, the only time I am introducing more than 3 birds is when I have a brooder full of "tween-aged" chicks to integrate into the flock. I've never brought home multiple adult birds.