How should an administrator manually validate the DNS readiness of a customer network?

According to the VxRail PEQ Engagement Details worksheet, links to what resources should the SE send to the customer?

Which requirement is optional for a VxRail Stretched Cluster?

You have been asked to deploy a single, 4 node VxRail cluster for company. They would like to migrate from their existing vSphere 6.5 environment. They have also asked that vCenter Enhanced linked-mode be supported.
Based on best practice, what is the recommended deployment model?

What is a permissible configuration when performing a cluster expansion?