How can I measure workload for sites and site groups?

As a national organisation with 500+ sites we need to assign projects and tasks to either large groups of sites or selected sites based on their characteristics. We also need to measure how much effort is involved for each site to absorb the change.

  1. The sites are not people with subscriptions so we can’t use this.
  2. Ideally when we assign a group of sites we can see the workloard for each individual sites.
  3. There was a suggestion to create dummy teams for each site. in this approach you can’t then add these to a group of sites because a team can’t be a member of a team.
  4. You can’t use tags, or drop downs because they are not an option to use in the workload view.
  5. It would be challenging to enter a high number of sites on each task without a group approach.

Has anyone solved?