To meet this requirement, a consultant should leverage Dynamic Lightning Pages, specifically using Component Visibility Filters. This allows for a declarative solution that does not require multiple page layouts or custom code.

Step-by-Step Implementation:

Edit the Page: Navigate to an Opportunity record and select Edit Page from the Setup (gear) icon to open the Lightning App Builder.

Add the Component: Drag the Related List - Single component onto the page layout.

Configure the Component: In the component properties sidebar, set the Related List to 'Engagement Plans.'

Set Visibility Filter: Scroll down to the Set Component Visibility section and click + Add Filter.

Define Criteria: * Field: Amount

Operator: Greater Than

Value: 10,000

Save and Activate: Save the page. When 'All Users' (per the requirement) view an Opportunity, the Engagement Plan related list will simply be invisible if the amount is $10,000 or less. If it is $10,001 or more, the component will appear.

Why other options are incorrect:

Option A: Assigning the page only to the development director's profile violates the requirement that 'all users' should see it when the criteria is met.

Option B: This is an overly complex and disjointed user experience that doesn't actually filter the view based on the specific Opportunity's amount.

Option C: A custom component is unnecessary 'Technical Debt' since standard functionality meets the requirement perfectly.