We moved into a place with an existing coop. We cleaned out the worst of it, sprayed down the entire thing with diluted bleach, waited a few days, repeated. Then just put in new bedding and never had an issue.
Regarding '6 or 7' a year... IMHO the most difficult part of raising chickens is the chick/pullet period. Once they're adult, it becomes very easy -food, water, gather eggs except for the occasional issue. Point being, once you get used to the chickens you may want to just bump up flock size to about what you want egg wise if you have the land/space. That said, having a variety of ages can be great so you don't have chickens all aging out at the same time.