To reply your first question: this is correct. Users at TL0 have certain permissions, while users at TL1 have all the permissions of TL0 plus some more. And so on for further trust levels.
For your second question: you should be able to see a list of users at TL0 at /admin/users/list/newuser (this is also accessible from the main admin dashboard in the “Users by trust level” table).