Charlotte, It all depends how how the product is used. The more customizations, integrations, add/change/delete of users/projects/custom pages/custom apps, etc. are used, the more Admin support they require. There must be at least one Subscription Admin (we recommend at least a second Sub Admin for emergency requests, vacations, continuity of service if one admin leaves, etc.). It also depends if your teams all operate the same or differently - this can add up to more administrative work and the need for Workspace and/or Project Admins to support those team differences. I know that's pretty vague, but I hope it helps. Please let us know if you have additional or more specific questions that we can address.
-Edwin