An administrator would enable Person Accounts during Order Management setup for the use case of connecting Order Management to B2C Commerce. B2C Commerce is a cloud-based platform that enables businesses to create and manage online storefronts for consumers. B2C Commerce uses Person Accounts to represent individual shoppers who place orders on the storefronts. Person Accounts are a type of account that combines account and contact information into a single record. To connect Order Management to B2C Commerce, an administrator needs to enable Person Accounts in Order Management and install the B2C Commerce Integration package from AppExchange. Reference: B2C Commerce Integration, [Person Accounts]

Three objects that are likely to get created in Order Management as an order progresses through its lifecycle are:
Fulfillment Order. 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.
Return Order. A Return Order is a record that represents a return request for an order or part of an order. A Return Order has a lookup relationship to both Order Summary and Change Order objects, and it contains information such as the return reason, status, date, etc.
Change Order. A Change Order is a record that represents a change request for an order or part of an order. A Change Order has a lookup relationship to the Order Summary object, and it contains information such as the change type, status, date, etc.
Verified Reference: https://help.salesforce.com/s/articleView?id=sf.order_management_fulfillment_order.htm&type=5 https://help.salesforce.com/s/articleView?id=sf.order_management_return_order.htm&type=5 https://help.salesforce.com/s/articleView?id=sf.order_management_change_order.htm&type=5

Explanation
Three objects that are likely to get created in Order Management as an order progresses through its lifecycle are:
Fulfillment Order. 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.
Return Order. A Return Order is a record that represents a return request for an order or part of an order.
A Return Order has a lookup relationship to both Order Summary and Change Order objects, and it contains information such as the return reason, status, date, etc.
Change Order. A Change Order is a record that represents a change request for an order or part of an order. A Change Order has a lookup relationship to the Order Summary object, and it contains information such as the change type, status, date, etc.
Verified References:
https://help.salesforce.com/s/articleView?id=sf.order_management_fulfillment_order.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.order_management_return_order.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.order_management_change_order.htm&type=5

One invoice will be created when using the Create Invoice Apex action in a flow. The Create Invoice Apex action is a custom action that creates an invoice for an order summary. An invoice is a document that requests payment from a customer for an order. An invoice can include one or more fulfillment orders and one or more credit memos. A fulfillment order is a record that represents a part of an order that is fulfilled by a specific location. A credit memo is a record that represents a partial or full refund for an order or a fulfillment order. An order summary can have multiple fulfillment orders and credit memos associated with it, but only one invoice will be created for the entire order summary. Reference: Order Management Objects, [Create Invoice Apex Action]

The correct statement about Person Accounts and Contacts is that Person Accounts are appropriate for B2C transactions while Account-Contact model is appropriate for B2B transactions. A Person Account is a type of account that represents an individual consumer, rather than a business or organization. A Person Account combines the features and fields of both the Account and Contact objects, and it does not require a Contact record to be associated with it. A Person Account is suitable for B2C transactions, where the customers are individual consumers who purchase products or services for personal use. An Account-Contact model is a type of data model that represents a business or organization as an account, and its employees or affiliates as contacts. An account can have many contacts associated with it, but a contact can only belong to one account. An Account-Contact model is suitable for B2B transactions, where the customers are businesses or organizations that purchase products or services for professional use. Verified Reference: https://help.salesforce.com/s/articleView?id=sf.accounts_person.htm&type=5 https://help.salesforce.com/s/articleView?id=sf.accounts_contacts.htm&type=5