Always have isolation/quarantine cages/pens to seperate them totally from the rest. I would seperate all first timers upon arrival, and seperate others as needed. Also monitor them as often as possible, watch closely for subtle changes, in eyes, beak-mouth,nostrils, breathing, movement, appetite, H2O intake, the sooner you find any problems the better for all involved. Have basic first aid kit on hand, (wound care (blue kote, neosporin, tape, gauze) respiratory disease (Vetrx at feed store it works very well if you catch eyes weeping, wheezing early on).. Have saved a ton of young uns (pullets) with it.
Had chickens 40 years, best advice is... Careful Where you get em. If you can't see where they come from, (pens, coops, barns) ya know like at flea markets, side of the road, ad in paper willing to meet you or deliver.. (Same goes with all animals, backyard breeders). Some folks just makin money or someone doing it for the animals, chickens, people and bragging rights to provide quality birds.. Disease is bad.. And spread quickly.
Good Luck in the future...