Hello KG.
In this case (seeing the amount of users, and the size of the archives), I would opt for exporting the archives to PST, then import them into the new EV.
There is no problem having 2 EV-sites targeting the same Exchange servers. You will have to make sure that you disable the users on the old EV, and make sure they are enabled on the NEW ev.
Then, when moving the archives, you will 'see' the targetarchives, and the shortcuts will be updated properly.
Move archive targets the EV-site, not the domain. So, site a in domain x will be able to mov to site b in domain x
moving archive is slow, but it is safe and secure.