Hi,
Insofar as best practices the following covers various scenarios - http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2021202
Of course you do have the option to upgrade your existing instance and move it to your new data centre (unless of course there's downtime constraints with that approach).
Regards a new build and slowly migrating hosts over for a new VC instance that will require a new set of DB's. Best in either case leaving your existing vcenter infrastructure separate from the new build