So let's assume that I do use the 2012 Essentials Version, and 2012 Standard joined to the domain, and the Essentials server failed. Would Starwind Virtual SAN still keep the data available even without Windows clustering? or is Starwind VSAN dependant on the FC feature of MS to function?

According to Xenserver forum, NFS and iSCSI have almost equal speeds even multipathed. Personally I think there is a limitations on any Unix solution and multipathing. Samba does not yet support multi-channel (But its been funded and someone is actively working on it.). Your post is the very reason ...

I did find a post that Server 2012 Essentials is supported for StarWind VSAN, however, it wasn't clear if Win2012 R2 Standard could be added to the Essentials domain and act as second node. I don't think failover clustering is included with Essentials, although MPIO and iSCSI are. Is that still poss...