Some thoughts about this:
- IMO it's a waste of resources to run all VMs on one host and have the other one just as a failover host. I'd recommend you run your VMs on both hosts, which will not only distribute the workload, but also has the advatage that - in case of a host failure - some of the VMs will survive.
- With the LUNs mirrored to the secondary NAS systems, ESXi will see both LUNs with the same signature an two targets. In this case one of the LUNs will be marked as a snapshot LUN and you will not be able to access it unless you mount it manually. Please ensure you only present the LUNs from the secondary NAS system in case the primary system is dead.
- With Essentials Plus and shared storage you also have the option to use vMotion (Live Migration). This can prevent downtime in case of host maintenance and help distributing the workload.
- How many NICs do you have in the system? With the setup you mentioned, I'd recommend a minimum of 6 NICs per host, two for Management/vMotion, two for iSCSI and two for iSCSI traffic.
André