Typically under Linux read only support is easy and while read-write support is possible it's not usually recommended. While OMV has tools for expanding data sets - you can install the LVM plugin for example and expand your LVM partition over multiple disks or install the zfs plugin - in my opinion the way they WANT you to manage it is multiple single disks or multiple static RAID sets of which you add more when you run out of room. Personally I feel that's safer anyway; I've never liked dynamically adjusting RAID arrays.
That hasn't been the case for years - most desktop distros will even offer to format external drives as NTFS 'cos it's more compatible with non-Linux-OSes than ext4 but doesn't come with the disadvantages of FAT32/VFAT. The only restriction I'm aware of with NTFS on Linux these days is that you can read from but not write to compressed files. (Writing to 'em just uncompresses 'em, so it's invisible to the user anyway.) Turns out ntfs-3g does compressed files these days, even. Nice. Debian's been using ntfs-3g (the driver that offers read/write support) by default since Squeeze came out in 2011. Nae bother.
Another long time UnRaid user here (4+ years), and I couldn't recommend it enough. Super easy to expand storage space, very very stable and very easy to migrate to new hardware. I've swapped out my underlying hardware (CPU, motherboard and RAM) twice now and never had any issues.
For NTFS-3G you can even set your linux UID and GID to match your windows ones (if you double boot for instance) so permissions remain consistent across the board. Check usermap.
