I've done a ton of migrations, and most of the advice I'd give has already been said in the other comments, except for one thing: If people are pushing for cha

I've done a ton of migrations, and most of the advice I'd give has already been said in the other comments, except for one thing: If people are pushing for changes to the app to better match how the business works today, leap into that conversation, but don't get talked into changing the app. Instead aim at reworking their business processes to first make their process as simple as possible, and then simplify the app to match the new process. Your migration is simpler when their process is simpler, and everyone wins. If people aren't willing to refactor business processes as part of the effort, then refuse to change requirements. Hold steady to "We both improve, or we stick to the status quo."