Windows and Linux are running 2 different file system .... which are basically incompatible to each other.... (NTFS for Win)
ZFS is a good choice. But the file system is not directly supported in Linux kernel and need to load external module. When you are looking for people to do the support and maintenance of your Linux, would that be even harder to hire someone? (It's probably hard to find experienced system admin, and you make the requirement even harder for someone with the experience of ZFS)
windows 7 pc can read/write linux EXT4 via SAMBA (should work with whatever file system on linux)
just config SAMBA permission on linux
easy (no AD) but not the best
another linux server with BackupPC to make full and incremental scheduled backups 7x24 from linux file server
easy restore files by simple ugly webUI