One idea is to use “invite links” and groups.
In the group settings you can adjust permissions and bestow trust levels.
Ie
- Group A:
- Regular employees of Dept A
- Group B:
- Regular Employees Dept B
- Group C:
* Managers & Supervisors
The benefits of groups you can use group access for Categories & in group settings have a member follow particular categories etc. If you think most should be TL2 or 3 the group can grant that trust level. Managers might get say TL4 etc..