We don't need to worry about introducing to existing stock (unless the cats count). We originally raised chickens in Tehachapi. So we've battled raccoons before.Chicks are often kept in a different type of housing before they are moved out to the regular coop, and tend to have less exposure to health issues. Bio-security is an important consideration with started stock as you do not want to introduce problems into your existing flock or brand new coop. Have you considered whether you want vaccinated chicks?
Haven't thought or talked about vaccination. Should probably do some research into that before we bring anyone home. We have managed to acquire a playhouse that will be transformed into a coop and a dog run that will be covered in chicken wire for the run.