Which method should be used to grant an unrelated group of users access to a set of records?

A custom ServiceFeedback object is used to collect partner feedback.
ServiceFeedback records should be available to all internal employees. The organization-wide default (OWD) is set to Private for external users so partners cannot see feedback from other partner users.
How should the architect give access to all internal employees?

An architect has a requirement to create a criteria-based sharing rule based on the customer Social Security Number. However, when setting up the rule in Contact Sharing, the field is not shown on the list of available fields.
What is causing this issue?

In order to allow community users to collaborate on Opportunities, which license type must the users be given?

Universal Containers (UC) has a team that analyzes customer orders looking for fraud. This team needs access to Invoice records (custom object, Private organization-wide default). UC has complex rules to control users' access. The architect recommended using Apex managed sharing to meet these requirements.
Which recommendation should a developer consider when implementing the changes?