I wish I would have check this thread sooner! I found that same PDF early in the afternoon.
This doc talks about a test bed of:
In the experiments, we used one vCenter host with a SQL Server database to support a representative vCenter
inventory in the ROBO environment. The vCenter had 640 total VMs in a configuration of 32 ESXi hosts and 20
VMs per host. The distributed resource scheduler (DRS) and high availability (HA) were enabled on the vCenter to
manage these hosts and VMs. Avirtual distributed switch (vDS) was created on the vCenterto manage the
network configuration of hosts and VMs. Each host and its 20 VMs were connected to an exclusive port group.
Since my config is so small and I don't understand really all the metrics and bandwidth, THEN combine that with my lack of true knowledge of how much bandwidth is at each of my sites I think my config of 2 hosts in each site and at most 4 VMs at each site I think one vCenter would work. One on the east coast and one on the west coast might even be overkill.