Hi Paul,
I will try to explain in a simplified manner -
a. If a licensed user creates a project, s/he can invite as many people as needed. The invited people will be able to access it only if they have a license. If the invited people are free users, they will see the project as locked and won't be able to view the content of the project (i.e., they wont be able to even open the project)
b. If a free user creates a project (max limit of 1 project), s/he can invite upto 5 other users. In this case, regardless of whether the invited people are free or licensed, they can access the project . They can upload / download , carry out actions such as - create ToDos, views etc.
By "read only" user not needing a license - if you are referring to a case - where a free user wants to only see the project content & details and not carryout any actions (such as upload / download / create & update todos etc) , we don't have such a functionality yet. Hope I am getting your question right. Please correct me if I am wrong.
Please let us know if further clarifications are needed.
Regards
Darshan Kamat