Congratulations on the transfer. Now that you've been through the process, you'll be the one giving advice.
And what a process it is! I'm sure there will be plenty more of these situations as the years progress, but at least he has a great opportunity now and is so excited to start the next chapter.
I don't know how good I'll be at giving advice, but I can surely share our experience and let people know how we handled it. It's been quite a roller coaster.
Good luck to all, in whatever comes!