The key questions to ask in this scenario are about the necessity of importing such a vast amount of historical data and whether the customer's license includes the Large Data Extensions feature. Understanding the customer's need for 10 years of historical data helps assess the relevance and potential performance implications for the Marketing Cloud environment. Additionally, knowing if the customer has the Large Data Extensions feature is crucial as it affects the capability to handle the significant volume of records efficiently. Reference: Salesforce Marketing Cloud Data Management documentation, Large Data Extensions feature specifications