The required amount of test code coverage when deploying an Apex class is 75%. This means that at least 75% of the Apex code must be covered by unit tests, and all of those tests must complete successfully. Verified Reference:https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_deploying_ant_deploy.htm

The number of Fulfillment Orders that would be created for this order is one per destination, totaling 3. A Fulfillment Order is a record that represents a group of products in an order that are fulfilled together from the same location. A Fulfillment Order has a lookup relationship to the Order Summary object, and it contains information such as the fulfillment location, delivery method, status, etc. The number of Fulfillment Orders created depends on three factors: Fulfillment Location, Delivery Method and Recipient Address. These factors determine how the Order Items are grouped and allocated to Fulfillment Orders based on routing rules and inventory availability. In this case, since the products must be shippedto three different locations, three Fulfillment Orders are created for each destination. Verified Reference:https://help.salesforce.com/s/articleView?id=sf.order_management_fulfillment_order.htm&type=5

Two steps that are required to add an item to the Actions & Recommendations panel on the Order Summary record page are:
Drag the Actions & Recommendations component on the page. The Actions & Recommendations component is a standard component that displays actions and recommendations based on business logic for records in Lightning Experience orSalesforce mobile app. The administrator can use the Lightning App Builder to drag and drop the Actions & Recommendations component onto the Order Summary record page layout.
Create a new sub-flow. A sub-flow is a type of flow that can be invoked by another flow as an element. A sub-flow can contain logic and actions that are specific to a certain scenario or use case, such as order fulfillment or payment processing. The administrator can use Flow Builder to create a new sub-flow that defines the actions and recommendations for Order Summaries, and then add it to the Actions & Recommendations component on the record page.
Verified Reference: https://help.salesforce.com/s/articleView?id=sf.om_actions_recommendations.htm&type=5 https://help.salesforce.com/s/articleView?id=sf.flow_ref_elements_subflow.htm&type=5

The correct time and way for creating an Invoice is at any point after the Fulfillment Order is created, by customizing flow "Create Invoice". This flow is a core action that creates an Invoice record from a Fulfillment Order record, and updates the status of both records accordingly. The administrator can customize this flow to suit their business needs,such as adding conditions, actions, or subflows. Verified Reference:https://help.salesforce.com/s/articleView?id=sf.flow_ref_elements_om_actions_create_invoice.htm&type=5