Answering my own question about the docker images, what I did was to use "Add Container" from the docker page for every image I wanted to add, then under "templates" I selected the template from the "users" section, created new containers with names in the form "sonarr-6-11", and set them to autostart instead of the old ones. The "add container" form had all the right data prepopulated correctly and so far everything has worked without a hitch.
thither's post in Most docker apps not starting after downgrade from 6.12 to 6.11, "Unknown subsys name 'elogind'" was marked as the answer