The question to ask before a warehouse migration
Not "can it move" but "what breaks if it does not". The second question produces a much shorter and more defensible first phase.
Warehouse migrations are usually scoped by inventory: list everything, estimate everything, sequence everything. The plan is comprehensive, the number is large, and the program is difficult to fund.
Invert it
Ask instead which workloads are currently costing you something that moving would stop. A renewal you do not want to sign. A batch window that has outgrown the night. A question the business asks that takes three days to answer. Those have a number attached already, which means the first phase pays for itself and earns the second.
Some workloads should not move
This is the part most migration plans leave out. A stable, cheap, well-understood workload with no growth and no dependency on anything you are modernizing is not a good early candidate, and sometimes not a candidate at all. Saying so early buys credibility for the recommendations that follow.
What a good assessment produces
Two documents. A sequenced plan that says which workloads move in what order and why, and a cost model honest enough to take to a CFO — including the workloads you are recommending against moving, and what it costs to leave them.
If an assessment produces only the first, it is a sales document.