Just a quick comment, the smart way to have done it would have been to build the new platform, copy the current database to it, get the new platform COMPLETELY functional, then shut down new orders for 24 hours, take another copy of the data base, load it to the new platform while shut down for 24 hours and then redirect the URL to the new platform at the end of the 24 hour shut down................but what do I know?
EDIT: Before someone gets their undies in a bunch, this is the fundamental outline of doing this, yes, there's a bit more involved, but it's been done and I've done it multiple times with larger companies. So I'm stick to my comment