I think your migration approach will work but think it is kind of complicated. Could you do something much simpler and just create a new Exchange 2010 Mailbox Server VM (on FC storage) and add it as an additional node in your DAG? You can add your databases as additional passive copies and then, when ready, switch them to active databases.
There are additional Exchange and Windows licenses required for that but to me at least it seems like a much less complicated method of moving the data while still giving yourself a fallback if you need it.
Anyway, just a thought. I think you've got a workable plan and you'll be successful either way. Good luck!
Matt