Party Identification Id is the only match criteria that is only available as custom in order to perform an exact match in Identity Resolution. Party Identification Id is a unique identifier for each Party Identification record in the data model. It is not one of the standard match criteria that Data Cloud provides out of the box, so it has to be created as a custom match criteria. Custom match criteria allow you to use any field from the data model as a match rule. References: Create Custom Match Criteria

The sales order subject area defines the revenue or quantity for an opportunity by product family. It also includes information about the opportunity stage, close date, and owner.References:https://help.salesforce.com
/s/articleView?id=sf.c360_a_data_cloud_sales_order.htm&type=5

This platform is going to present a challenge in terms of connection limits forData Cloud. Data Cloud supports up to 3 Marketing Cloud connections per org, which means that only 3 Marketing Cloud accounts can be connected as data sources or activation targets. The other platforms have higher or no limits for connections. References:https://help.salesforce.com/s/articleView?id=sf.c360_a_data_cloud_limits.
htm&type=5

The Email field from a CRM Contact object should be mapped to the Contact Point Email entity in the Customer 360 data model. This entity represents an email address that is associated with an individual or an account contact. References: [Contact Point Email Entity]