Add the standard Chatter feed component is how an app builder can add the Chatter feed to a custom object record page. According to the Salesforce documentation, "The Chatter Feed component displays updates about records in your org." Add the standard related list component, add a custom Chatter feed component, and add the Chatter feed component from the AppExchange are not valid or necessary options.

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.

An indirect lookup relationship is a custom relationship between two objects that are linked by an external ID field. The external ID field must be a custom field on the parent object that has the "External ID" attribute enabled. The child object must be a standard or custom object that is on the detail side of a master-detail or lookup relationship.

The app builder should create a new roll-up summary field called First Order Date, using Type MIN on the Opportunity Close Date with a filter where IsWon = TRUE. A roll-up summary field is a type of field that calculates values from related records and displays them on the parent record. In this case, the app builder can create a roll-up summary field on the Account object that calculates the minimum (earliest) value of the Opportunity Close Date field from the related opportunities where IsWon = TRUE. This will show when customers made their first purchase. Option B, C, and D are not correct ways to use a roll-up summary field to meet the requirement.

The app builder should use Apex code to update a field on the parent record when a child record connected via lookup is deleted. Apex code is a programming language that allows developers to execute complex logic on the Salesforce platform. Apex code can be triggered by certain events, such as insert, update, delete, or undelete of records. In this case, the app builder can write an Apex trigger that runs after a child record is deleted and updates a field on the parent record accordingly. Option A, B, and D are not automation tools that can perform this task.