Sorry, I was just throwing ideas at you.
ZFS is your best choice. Snapraid isn't a live solution - it'll run a job at intervals. Good for static data, but little use for your requirements and probably not worth the hassle.
https://pve.proxmox.com/wiki/Storage:_ZFS#Administration suggests that ZFS is purely a command line solution, unsurprisingly. When you say that it'll need to be useable by other people, what do you mean? I'm guessing just Samba/CIFS access, in which case the underlying filesystem has no effect either way.
As previously mentioned, use a standard filesystem for virtualisation, and ZFS for all direct data storage (i.e. not VM images). Sharing would work as previously mentioned (shared directories via VirtFS).
Honestly, your requirements exceed those of the majority of home NAS users. It might be easier to get yourself comfortable in the command line and configure this manually rather than using Proxmox - heck, install CentOS with a GUI and use virtmanager via VNC just like you would on your desktop if you don't want to touch the command line unless absolutely necessary.
I've personally found these pretty-GUI solutions fairly frustrating unless you use them exactly as intended. You'll likely find the same to be true.
