How would I use a plan showing 500 social accounts, 200 seats, and 200 workspaces?

Those are three separate capacities, not 500 social accounts for each of 200 people. For example, ten client workspaces with five social accounts each use 50 of the 500 social-account slots and ten of the 200 workspaces. Invite collaborators to the relevant workspaces and assign their roles. You do not need to use every seat or workspace. This is an illustrative example; use the allowances displayed on your own billing page.