Let me give you the full specs of each vm
the 2 ESXi
2gb ram
2 vcpu
40 gb hdd
Network Adapter 1 - Bridge(Management and prod)
Network Adapter 2 - Hostonly (iSCSI)
Network Adapter 3 - NAT (vMotion)
Network Adapter 4 - Bridge(Management Redundancy)
Network Adapter 5 - Hostonly(iSCSI secondary. Yes i have dual path in my lab)
the vCenter Appliance
4gb ram
2 vcpu
25 GB hdd1
60 GB hdd2
Network Adapter 1 - Bridge
OpenFiler
256mb mem
1 vcpu
and disks 12 gb for root and you can specify anything for the volumes you'll use as iscsi targets.