I can't find this anymore on the VMware web sites, but in the past VMware offered an upgrade from Essentials or Essentials Plus to an Acceleration Kit, which included vCenter Server Standard as well as 6 CPU licenses (Standard, Enterprise or Enterprise Plus, depending on the selected option). I'd suggest you contact a VMware partner/reseller and ask for such options, e.g. one upgrade to a Standard Acceleration Kit plus 12 additional CPU licenses.
Btw. unless I'm mistaken Essentials Plus also allows to live migrate VMs including the storage using the vSphere Web Client. Maybe that's an option for you?
André