Explanation
Before disconnecting the sandbox instance and connecting the production instance in the Cloud Kicks business unit, NTO should remove any existing user mappings, attribute mappings, and tracking subscriptions that are associated with the sandbox instance. User mappings define which Marketing Cloud users can access which Sales Cloud users' data. Attribute mappings define which Sales Cloud fields are used as subscriber attributes in Marketing Cloud. Tracking subscriptions define which Sales Cloud objects receive tracking data from Marketing Cloud sends. These settings should be removed before changing the CRM connection to avoid errors or conflicts. Additionally, NTO should update any query activities that reference the synchronized data extensions from the sandbox instance, as these will be different from the production instance synchronized data extensions. References:
https://help.salesforce.com/articleView?id=sf.mc_co_disconnect_a_salesforce_org_from_a_business_unit.htm&
https://help.salesforce.com/articleView?id=sf.mc_co_map_marketing_cloud_users_to_salesforce_users.htm&typ
https://help.salesforce.com/articleView?id=sf.mc_co_create_attribute_mappings_for_your_account.htm&type=5
https://help.salesforce.com/articleView?id=sf.mc_co_set_up_tracking_information_to_send_to_salesforce.htm&

Explanation
The Contact ID field name should be included in the report in addition to email address when using a Send Flow in Content Builder. The Contact ID is a unique identifier for each contact in Sales Cloud and Marketing Cloud. It is required for sending emails to contacts using a Send Flow. The other field names are not required for this purpose. References: https://help.salesforce.com/s/articleView?id=sf.mc_co_send_flow.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.mc_co_contact_id.htm&type=5