Using hard delete in Bulk API, identifying records that have not been modified or used in last 3 years, and archiving the records in EDW before deleting from Salesforce are all good recommendations to reduce the number of records from the org1. Using hard delete in batch Apex or Rest API may not be as efficient or scalable as Bulk API

The best Salesforce Shield capabilities for the customer are to restrict access to SF from users outside specific geography, implement transaction security policies to prevent export of SF data, and encrypt sensitive customer information maintained in SF. Salesforce Shield is a set of security features that help protect enterprise data on the Salesforce platform. It includes three components: Event Monitoring, Platform Encryption, and Field Audit Trail. Restricting access to SF from users outside specific geography can be done using network-based security features, such as IP whitelisting or VPN. Transaction security policies can be used to define actions or notifications based on user behavior patterns, such as exporting data or logging in from an unknown device. Platform Encryption can be used to encrypt data at rest using a tenant secret key that is controlled by the customer.

Using a declarative approach by installing and configuring Data.com Clean to monitor Account data quality can help UC meet their requirement. Data.com Clean can enrich and cleanse data on an ongoing basis by comparing Salesforce records with Data.com records and providing suggestions for updates. Data.com Clean can also provide dashboards and reports to monitor key data quality metrics such as match rate, field fill rate, and record completeness