Reviewing the MKTO product docs, I see that MKTO recommends building smart lists and using Special--> Change Revenue Stage action. See at Approving Stages and Assigning Leads to a Revenue Model - Marketo Docs - Product Docs
I have done this thru building batch (retroactive) campaigns and assigning leads to the correct revenue stages. I don't believe there is an advantage that one has over the other, but wanted to see if I am missing anything. Thank you.
Yes, use batch flows to backfill people. Not sure how else you would do this.
Do not use Single Flow Action as shown because it is impossible to figure out what happened later in case there's an error.