iscsi Windows Server hyper-v cluster

Per Microsoft recommendations https://technet.microsoft.com/en-us/library/jj612868(v=ws.11).aspx you should consult your storage vendor that may recommend configuring each LUN with one partition and place one CSV volume on it.

Generally, I would recommend having iSCSI LUN and CSV numbers equal to hypervisor hosts. You can bound each cluster shared volume (iSCSI LUN) and virtual machine to one hypervisor host to be sure that if both cluster nodes are running all the resources are spread equally across the cluster and migrate only in case of failover.

Going a bit further Microsoft recommends having different CSVs for virtual machine’s system partition and data drives that may result in 4 CSVs in your case which is an overkill I guess.

Since each of iSCSI LUNs and cluster shared volumes is accessible by all hypervisor hosts (as shared storage) you can easily migrate your virtual machines between hosts and between CSVs if needed.

I would strongly recommend you to create one more virtual machine as a secondary DC. If your physical DC fails (or goes down for maintenance) there is a great probability of losing the whole cluster too. And don’t forget to configure failover cluster witness drive (or share). Your physical DC is a good option for this purpose however Microsoft recommends having witness clustered/cloud to be highly available too.

IMHO granular LUN configuration is still the best way to properly distribute workload within an environment. This will really make the management easier, and I think it makes sense for any environment. But in you case, I would just distribute the VMs by type of workload or something.