Which community function is impacted by having the Site User Visibility turned off in Sharing Settings?

Universal Containers (UC) operates worldwide, with offices in more than 100 regions in 10 different countries, and has established a very complex Role Hierarchy to control data visibility. In the new fiscal year, UC is planning to reorganize the roles and reassign account owners.
Which feature should an architect recommend to avoid problems with this operation?

Universal Containers (UC) would like to store an encryption key within Salesforce for use in Apex code, but it does not want users to be able to see this confidential key. Users require the view setup permission.
How can UC securely store the confidential key?

To grant Universal Containers sales managers access to shipment records properly, it was necessary to leverage Apex managed sharing. The IT team is worried about improper access to records.
What should an architect recommend to mitigate this risk?

Universal Containers is implementing Sales Cloud. During the final quarter of the financial year, sales managers help each other close deals. They requested a solution in Salesforce to allow them to share opportunities with other sales managers from different teams as needed. They also requested that sharing deals should expire automatically 2 weeks after the new fiscal year starts.
Which proposed solution meets the requirements?