Explanation
The consultant should set Account and Contact's sharing to private before the data load, and disable all TDTM trigger Handlers before the data load, to load a large volume of alumni contact records into a new Salesforce environment. Setting Account and Contact's sharing to private before the data load can prevent sharing recalculation and improve performance. Disabling all TDTM trigger Handlers before the data load can prevent unwanted automation and validation from running and affecting the data load. Setting Account and Contact's sharing to public Read/Write before the data load, or loading record owners after the Account and Contact data load is complete, are not actions that the consultant should take. References:
https://help.salesforce.com/s/articleView?id=sf.data_loader_tips.htm&type=5
https://powerofus.force.com/s/article/EDA-TDTM