Hi
You are on right track .
A. Install new esxi
B mount the NAS box
C. configure the Networking
D ensure you are able to access the datastore which has VM's
E. If everything looks good, shut down the VM , remove from inventory of ESXi (old)
F. Browse the datastore for a VM and right click on VMX file and add to inventory on new esxi host. Power up the VM. Follow this for all other VM's
G. Once all the VM's are migrated , power down the old ESX host and remove from the network.
Cheers :-)