Implementing a Contact Conference junction object with master detail relationship to both contact and conference_c is the correct way to model the relationship between the contact and conference objects, as it allows a many-to-many relationship between them. This means that each contact can attend multiple conferences, and each conference can be related to multiple contacts. Creating a master detail relationship field on either the contact or the conference object would create a one-to- many relationship, which does not meet the requirements. Creating a lookup relationship field on contact object would also create a one-to-many relationship, and would not enforce referential integrity.

Single-select restricted picklist with defined choices can be a way to configure customer type. The article states that picklists are fields that allow users to select one or more predefined values from a list, and restricted picklists ensure that users can only select from the defined values. This can help to limit the choices for customer type and ensure data quality.

Specify the legacy CRM as the system of record during transition until it is removed from operation and fully replaced by Salesforce. This is a good technique to ensure data consistency and avoid conflicts between the two systems. Work with stakeholders to establish a Master Data Management plan for the system of record for specific objects, records, and fields. This is another good technique to define the data governance and stewardship policies and processes for managing data quality and integrity across multiple systems.

A junction object enables many-to-many relationships by using two master-detail relationships.

Using Salesforce Bulk API in parallel mode can reduce the migration time by processing multiple batches of records simultaneously and leveraging the server resources more efficiently. The Bulk API is designed for loading large amounts of data into Salesforce