I need all the same requirements as you pretty much, and I am torn between freenas and openmediavault
Have been using FreeNAS for some time now with no issues.
FreeNAS 11 has the ability to use kvm, so it covers anything like VPNs if you cant use a FreeBSD jail.
It has plugins for Plex/Sonarr etc, and I'm slowly following a guide here
For offsite backups tarsnap or crashplan are both pretty good options, and the I've seen the FreeNAS community build jails to accommodate them if needed.
It does prefer ECC RAM and ZFS can take a bit of getting used to, but mine has been working without issue for over a year now.
OpenMediaVault is similar, more plugins, debian based (most likely easier than freebsd), and a little more friendly, but it just didnt seem to have the optimization that FreeNAS has.