ReadyNas Pro and Xencloud/Xenserver

So I support my church afterhours and in the process of upgrading hardware/software and planning on going to xenserver/xencloud to handle the the new servers. Planning on going with sbs 2011 and we also have a couple of other servers linux based doing image management, etc. So I have been reading all weekend on NAS hardware and performance, while I realize that performance will not be as good as if the storage was native to the box, I am considering putting all of the Data pools on the nas, they will be connected to the same switch gig speeds and contemplating whether to go iscsi or nfs. Looking at the naspro 4 or maybe the naspro 6 and my preference would be to run in flexraid mode and run raid 10. Actually my preference would be to run Raid 10 + hotspare in the Naspro 6 but I can't see anywhere that this is supported at the moment. We are talking about small number of users 5-10, so I think performance would be acceptable unless someone can tell me otherwise. The other thing that I am trying to figure out is if I put all of my VM's on the NAS, what is the best way to back them up/replicate them to another NAS etc. I can shut the vm's down and perform snapshots, right now we do backups three times a week to a usb hard drive that is rotated offsite. What I am trying to figure out is what is the best way to achieve this, I was thinking of purchasing a readynas pro2 and use the replicate function but its not clear if I could schedule this to replicate only when the vm's are offline. If anyone has any suggestions/thoughts I would greatly appreciate the input, Thanks :)