If you are starting "net new" then it's pretty straight forward. If it were me, I would start from scratch even with your vCenter. Build it as a VM, side by side with your older instance. This way you can document any roles and permissions, virtual machines and templates folders, DRS rules, etc....
Create your new SQL instance ensuring you have dbo on both the VCDB and the MSDB (to create rollup jobs). Once your new vCenter instance is on-line got to the main toolbar and choose Administration--vCenter Server Settings. You can add in your VI3 vCenter Server as the license source for your VI3 Hosts.
When complete, just disconnect and remove the host(s) from the old environment into the new. You can then shutdown your old vCenter Server Service but leave the license server running. Or build a standalone license server...either or.