Create a custom action is the recommended solution to meet the requirement of creating additional accounts to form a hierarchy from a Parent Account record. According to the Salesforce documentation, "Actions let users quickly create or update records, log calls, send emails, and more, in the context of a particular object." A custom action can auto-populate fields based on the parent account and make it easier for users to create child accounts. Add Path on Account hierarchy, add a custom link on Account, and customize a Global Quick Action are not valid or feasible options.

An external ID field can be a number field or a text field, but not a URL field or a phone field. A URL field is used to store web addresses and a phone field is used to store phone numbers. An external ID field is used to store unique identifiers from an external system and it can be used for upsert operations

Guided Action Flows on the record page can help service agents meet the requirement of confirming a user identity before providing support information over the phone. Guided Action Flows are a series of screens that guide agents through a predefined process, such as verifying user information, collecting case details, or resolving issues

Update the organization-wide defaults and create a criteria based sharing rule are two actions that an app builder should complete to implement the change of moving to a more restrictive sharing model while allowing the Sales team to access all account records with the sales record type. Updating the organization-wide defaults can set the baseline level of access for accounts, and creating a criteria based sharing rule can grant additional access based on record type. Updating the Sales profile and creating an owner-based sharing rule are not necessary or sufficient actions for this change.

Putting the SC in the role hierarchy above the technicians whose work orders they review will provide the required access, given a private data model. The role hierarchy determines how users can access records they do not own. Users at any given role level can view, edit, and report on all data owned by or shared with users below them in the role hierarchy.