docker storage backend and container-generated data storage

I am learning about Docker storage and I am little bit confused about

Question 1 :
Do we have for each docker host 1 backend store ( to store layers of images and writable-layers of containers ) ?
and if configured we’ll have also a container-generated data store ( to persist the data wrote by a container (Volumes,Bind mounts,tmpfs mounts) ) ? or do we have both by default ? or there is just one unique store ?

Question 2 : suppose we have configured a volume to persist container-generated data , is it still gonning to be a a union fs layer somewhere else that is going to be persisted even if the container is removed ?

Question 3 : containers are runnable images , but concretly can you explain to me what are they ? are they just a unionFs layer ?

Question 4 : if we uninstall or stop docker is the thin pool on loopback device used by default for the storage backend , is it saved or is it removed ? and what if we configure a thin pool on a logical volume and we uninstall docker will we still have the images and the container-generated data on the logical volume ?

Question 5 : how do we configure docker to use a group volume ( or a logical volume ) in a remote machine ?

Question 6 : what is the different between the persistant storage configured for kubernetes/okd/openshift cluser and the persistant storage configured for docker

Source: StackOverflow