That's a pretty serious amount of storage and thus a pretty serious project / problem to solve.
If you want to be in the business of running a file server using cheap commodity PC hardware, I'd set up an OpenSolaris box and set up the first group of roughly size matched drives into a RAIDZ group with one drive redundancy unless you prefer RAIDZ2 for two drives worth of redundancy.
When you go to expand the storage pool you can just add another group of 3 or more drives at once adding a second independent RAIDZ group to the existing overall storage pool. The filesystem you have created / shared will magically be able to expand to use the added capacity in the pool and still appear as one / the same filesystem with no further administration needed.
http://www.opensolaris.org/os/.../zfs/docs/zfs_last.pdf
http://docs.sun.com/app/docs/doc/819-5461
http://opensolaris.org/os/downloads/
http://opensolaris.org/os/downloads/sol_ex_dvd_1/
# Create a RAIDZ of four drives (any three or more will do) and put them in pool StoragePool
zpool create StoragePool raidz c1t0d0 c2t0d0 c3t0d0 c4t0d0
# Create a filesystem in the storage pool
zfs create -o casesensitivity=mixed -o nbmand=on StoragePool/BigFileSystem
# Set the mount point (path to access) the new filesystem
zfs set mountpoint=/export/BigFileSystem StoragePool/BigFileSystem
# Enable NFS and SMB (CIFS i.e. for Microsoft Windows systems to access it ) sharing on the filesystem
zfs set sharenfs=rw StoragePool/BigFileSystem
zfs set sharesmb=on BigFileSystem
# Later on we add four (or any three or more) more drives by creating a new RAIDZ of these new four and adding them to
# the existing storage pool StoragePool. Since the pool's free space just grew, so can the filesystem(s)
# defined to use the pool, so voila you have more space in the pool and the filesystem just stays
# available just as before except with more free space.
zpool add StoragePool raidz c5t0d0 c6t0d0 c7t0d0 c8t0d0
If you'd rather have less administration to do, buy a storage server or good NAS RAID unit and use it.
Personally I wouldn't trust 8+ TB of my data to Windows Home Server.
MAYBE WINDOWS SERVER 2008 with a GOOD hardware RAID card... but unproven / immature and still sort of unstable Windows Home Server? Uh no thanks.