VMware vSphere Essentials Kit Question

Hi All, I'm looking into purchasing the VMware vSphere Essentials Kit. I know its a 3 host, 2 socket per hosts but, my question is that the 3 servers I have are running all different versions of Vsphere. They are all Cisco UCS C series servers.....all have a valid Vsphere license. I have a mix of version ESXi 4, 5.5, and 6.5.

If I buy this licenses will I be able to manage them all since they are all different versions? Also is the Vcenter server that comes with this kit an appliance/ova?

Thanks,

Mike