ACD licenses are consumed per logged-in ACD user, so you do not need a license for each potential member of the queue, but you need to know the maximum number of concurrent logged-in users.
For example, if a customer has a customer service ACD group where they need 20 users to answer calls, but these 20 users work different shifts so that only 10 users are logged in at the same time, then the customer needs 10 concurrent ACD Agent licences that are sufficient, rather than having to buy a license for each of the 20 users.
The ACD Supervisor licence is an organisation-specific licence, that is required when the customer needs even a single ACD Supervisor user.
In that case it will increase the price of each ACD Premium level license, which means that the price is paid according to the number of users supervised, not the number of supervisors.
Comparison of ACD Groups licensing levels:
