Control Panel For Email Serices

I want to develop a control panel to manage paid email services for companies, it will be just one control panel on my domain and each company has the ability to log in to their account and manage their email services (creating accounts, deleting ones, add users, quotas, etc) now my question is which license should I pay for when I buy Admin templates?

My client pay Just for the email service and they login to manage their emails from my domain.

Thanks in advance!