I have a 2(3) server setup that does exactly what you are looking at doing.
-File Server(I have HP Microserver Gen7 running Oi/Nappit)
-HP Microserver Gen8 with Xeon 1230 swap running Hyper-V
Hyper-V box runs 2 domain controllers and a Plex VM. I stream 720/1080 to Rokus and xbox360s...
Do you have a lot of customization in the template definition?
Convert the template to a VM, export it as an OVF, then convert the VM back to a template. Import the OVF to the other system and recreate the customization spec.
If your san supports it, look into VVOLs for servers that tend to be problematic with the snapshot removal process. We had a number of VMs that would take almost an hour to remove the snapshots and it was killing our SAN IO.
For my home setup I went this route:
HP Microserver Gen8 running Hyper-V with 2 DCs and a Plex server
Norco ZFS box running openindiana/nappit on bare metal.
I've played with all-in-one/passthrough in the past, but it was more hassle than it's worth. If I need more compute I can set up an...
If you're going ESXi, get a 16-32gb small footprint thumb drive for the OS. Most modern motherboards will even have a USB port directly on the motherboard for this purpose. For the raid, make sure you have a real raid card, and not softraid.
Instead of using the keep VMs together rule try a host affinity rule with the "should keep VMs together". This will allow the VMs to migrate off during patching, then migrate back when the host exits maintenance mode.
We've been using 10g iSCSI in production for the last 4 years with no issues.
The twinax cable is essentially a copper cable with built-in SFP+ modules.
The FreeNAS FC method looks extremely hackjob and not a representation of real world FC.
I would recommend checking ebay for intel X520 10GE based cards and snagging some passive twinax cables, much less frustrating in the long run.
Most modern motherboards have an onboard USB port, or you can get an adapter to use one of the USB header ports. No need to have a USB port hanging off an external port.