A data quality problem that could cause customers to be called by multiple Sales Reps is having duplicate Contact records in the system. Duplicate records can result from data entry errors, data imports, or integrations with other systems. Duplicate records can lead to confusion, inefficiency, and customer dissatisfaction.

To help uniquely identify customer across multiple systems, a data architect should recommend creating a custom field as external ID to maintain the customer ID from the MDM solution. An external ID is a custom field that has the "External ID" attribute enabled, which means that it contains unique record identifiers from a system outside of Salesforce. By using the customer ID from the MDM solution as an external ID in Salesforce CRM, Contract Management system, and Marketing solution, the data architect can ensure that each customer can be easily identified and integrated across these systems.

Bulk API is optimized for large-scale data loads.

The best data archiving strategies for UC are to use Big objects and Heroku with external objects.
Big objects allow storing large amounts of data on the Salesforce platform without affecting performance or storage limits. They also support point-and-click tools, triggers, and Apex code.
Heroku is a cloud platform that can host external databases and integrate with Salesforce using external objects. External objects enable on-demand access to external data sources via standard Salesforce APIs and user interfaces. Using bulk API to hard delete cases from Salesforce will free up storage space and improve performance.

Partner community license type is the best option for building a channel sales portal, as it allows external resellers to access lead, opportunity, and order data, as well as run reports and dashboards. Customer community and customer community plus license types are more suitable for customer service portals, while lightning external apps starter license type does not support reports and dashboards