The best Lightning component to add to the layout to display the 'New Task' custom action is Highlights panel. This component shows key information and actions for a record, such as its name, owner, and custom actions. Related record, related lists, and activities are not Lightning components that display custom actions. See [this article] for more information on Highlights panel.

To control access to the Review custom object such that only the HR department and the submitting employee can see the reviews, the following steps should be taken:
A . Disable Grant Access Using Hierarchies:By default, Salesforce allows users higher in the role hierarchy to access records owned by users lower in the hierarchy. Since reviews should only be visible to HR and the submitting employee, you need to disable Grant Access Using Hierarchies on the Review object to prevent anyone else in the hierarchy from automatically gaining access to these records.
Record Access and Role Hierarchies
C . Create a criteria-based Sharing Rule for the HR Department:With the organization-wide default (OWD) set to Private, you'll need to create a criteria-based sharing rule to ensure that HR users can view the Review records. This rule would give HR access to the records based on a specified condition, such as all records of the Review object.
Reference:
E . Set organization-wide default to Private:Setting the organization-wide default (OWD) for the Review object to Private ensures that no user, other than the record owner (the submitting employee) and those explicitly granted access (HR), can see the Review records by default.
Why the other options are incorrect:
Option B: Add a Master-Detail (User) field on the Review object:This is not necessary in this scenario because the primary relationship is about controlling access through sharing rules, not creating a master-detail relationship. Moreover, this would complicate access control, which is better managed via sharing settings.
Option D: Remove Review Read permission from non-HR Department user Profiles:This step is redundant if the organization-wide default is set to Private. Profile permissions control the general ability to access the object, while the visibility of specific records is controlled by sharing rules and OWD. Removing read access via profiles would block all users, including the ones submitting the reviews, from accessing the object.
In summary, by disabling Grant Access Using Hierarchies, setting OWD to Private, and implementing a criteria-based sharing rule for HR, you can ensure that only HR and the submitting employee can view Review records.

Workflows that cause each other to fire back and forth recursively can result in workflow limits errors. For example, if workflow A updates a field that triggers workflow B, and workflow B updates a field that triggers workflow A, this can create an infinite loop of workflows that exceed the maximum number of workflow time triggers per hour.

To manage field editability based on the opportunity status:
C . Use field-level security on page layouts with record types to restrict editing fields. This combination allows for different layouts and editable fields based on the status of the record (e.g., closed or open).
Steps to implement:
Create or adjust record types for open and closed opportunities.
For each record type, create a specific page layout.
On the page layout for closed opportunities, set the majority of fields to read-only using field-level security, except for the 'Post-Close Follow-up Date' and 'Post-Close Follow-up Comments' fields.
Assign the appropriate page layouts to the respective record types.
Update profiles or permission sets to use these record types and page layouts accordingly.
This setup ensures that sales reps can modify fields only when the opportunity is open, and the sales operations team can edit specific fields after closure.
For more information on using record types and page layouts, check Salesforce's documentation on Record Types.

The inability to create a Roll-Up Summary field in this context can be attributed to:
B . The organization has Advanced Currency Management enabled. When Advanced Currency Management (ACM) is enabled, it affects how currency data is managed and aggregated, impacting the functionality of roll-up summary fields that involve currency amounts across different records.
To address this limitation, consider using custom reporting or a custom solution like a trigger or a scheduled batch class to manually calculate and update the total.
For more information on limitations with ACM, consult Salesforce's help article on Advanced Currency Management.