1. As per licensing guide, write access to the custom entities have below constraint. Does it mean that if there is a relation with the custom entity and OOB entities that isn't part of the team member's license like opportunity, case etc, then that custom entity becomes inaccessible to TM users?
*** Custom entities (either based on entities included in Microsoft Dynamics 365 or created by a customer or partner) may require a higher CAL or User SL, depending on the required access. Customizations can only be performed against entities included in the use rights.
2. Is there any limitation to the number of custom entities that Team Member license users can access?
3. Sample scenario: Agents and equipment are resources in my scenario where agents have TM licenses and the office users are power users. I'm planning to store the agents or equipment in the Field Service's resource entity so that my office users can schedule them in the schedule board. The agents will be using PowerApps mobile app to report an issue (custom entity). The tricky part is the agents will also use the PowerApps mobile app to reassign their work to another agents (resource entity) for which the TM license doesn't have access to. 
Is there any work around to implement this where agent can use another agent's record with TM license.?
Thanks,
Jeeva