Document your considerations and efforts. What worked, what didn’t. Recruit a few of them that did and didn’t migrate for a post-conversation to find out why, so that in the future we can eliminate hurdles. Document it from a tech perspective, as well as from a user experience perspective. Smoothness with onboarding is a critical workflow that needs special attention, because people are finicky with what they will and won’t do, and what were their reason why they did or didn’t.