Thank you for your reminder Scott28tt,
Yes I will buy more than one ESXi 8.x server for the HA and failover.
Will using vMotion/Cold vMotion for mirgate the VM(s).

Background
Over 10 ESXi 6.7 Server need to migrate to new purchase (assume 7-9) servers and install ESXi 8.0
On old ESXi 6.7 over 200 VM(S), total using over 900 CPU and over 3000GB RAM

Query
For the VM population grow, I need clarify the calculation method then estimate the Qty for migration (I will take some buffer for overload)