Counting units for GitHub Marketplace Apps

Our team is developing an app for GitHub Marketplace. We are a bit confused about counting units for pricing plans.

For example, we might want to set flat rates for a certain amount of users or Git authors - or make a per-unit plan based on the same. Do we get this information (number of users or number of authors) via GitHub Marketplace API, or do we have to count them within the app?

Also, if we have a special plan for organizational accounts - do we receive the number of users within an organization from the API?