Easy Projects is licensed based on the total number of active (not disabled) user accounts with the "Can login" option enabled.
E.g. if you need 10 different users to have their own logins, you need to get one 10-user license.
Any disabled user account and account that cannot login does not count against total number of user licenses.
E.g. if you have 6 enabled accounts, 3 disabled ones and 2 which cannot login, you need to have a license only for 6 users.
You can purchase additional user licenses any time you want.
Please note that Guest users (previously Limited Access users) do not require licenses, you can create as many ones as you need.