According to the Salesforce documentation4, Marketing Cloud is a platform that allows creating and managing marketing campaigns across multiple channels, such as email, mobile, social media, web, etc. Marketing Cloud can integrate with Sales Cloud and other Salesforce products to share data and insights. One of the ways to integrate Marketing Cloud with Sales Cloud is using Marketing Cloud Connect5, which allows syncing data between the two platforms using synchronized data sources.
However, if UC occasionally gets a list of prospects from third-party sources as CSV files for marketing purposes, it may not be necessary or efficient to load them into Sales Cloud first and then sync them with Marketing Cloud. This can consume large amounts of storage in Sales Cloud, which has a limit based on the license type6. It can also cause data quality issues, such as duplicates or outdated information.
A better option for UC is to load the contacts directly to Marketing Cloud using Import Definition, which allows importing data from external files or databases into Marketing Cloud data extensions. Data extensions are custom tables that store marketing data in Marketing Cloud. This way, UC can avoid storage issues in Sales Cloud and optimize the marketing process by sending marketing communications directly from Marketing Cloud.
To track prospects that are converted to customers, UC can have a reconciliation process that compares the contacts in Marketing Cloud with the accounts or contacts in Sales Cloud. This can be done using SQL queries or API calls to access and compare data from both platforms. Alternatively, UC can use Marketing Cloud Connect to sync the converted contacts from Sales Cloud to Marketing Cloud using synchronized data sources.
Loading the CSV files in Einstein Analytics and syncing with Marketing Cloud prior to sending marketing communications (option A) is not a good option, as it can add unnecessary complexity and latency to the process. Einstein Analytics is a platform that allows creating and analyzing data using interactive dashboards and reports. It is not designed for importing and exporting data for marketing purposes.
Loading the CSV files in an external database and syncing with Marketing Cloud prior to sending marketing communications (option B) is also not a good option, as it can incur additional costs and maintenance for the external database. It can also introduce data security and privacy risks, as the data may not be encrypted or protected by Salesforce.
Continuing to use the existing process to use Lead object to sync with Marketing Cloud and delete Lead records from Sales after the sync is complete (option D) is not a good option, as it can cause performance issues and data loss. Deleting Lead records from Sales can affect reporting and auditing, as well as trigger workflows and validations that may not be intended. It can also cause data inconsistency and synchronization errors between Sales Cloud and Marketing Cloud.

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 license to provide these features to the franchisees is the Partner Community license. Partner Community licenses are designed for external users who collaborate with your sales team on deals, such as resellers, distributors, or brokers. Partner Community users can access standard CRM objects, such as accounts, contacts, leads, opportunities, campaigns, and reports. They can also access custom objects and run dashboards12. Salesforce Sales Cloud license is not a good option because it is intended for internal users who need full access to standard CRM and custom apps. Lightning Platform license is not a good option because it is intended for users who need access to custom apps but not to standard CRM functionality. Customer Community license is not a good option because it is intended for external users who need access to customer support features, such as cases and knowledge articles, but not to sales features