1. if the devices on your list can access (browse, read, and write) a windows share folder, you can make pogoplug+arch linux to share files to all those devices since windows share and samba share use the same network protocol (SMB [wikipedia.org]
). exFAT is not the issue here since to the clients, the shared files are treated as network filesystem (SMB/CIFS) instead of local filesystem (ext2/3/4, ntfs, exFAT) so the OS vs. filesystem compatibility is not the issue here (as long as they can access the shared files, there is no filesystem problem except the character coding system).
2. Put all media files under a folder on one external drive and share that folder.
3. You don't have to install archlinux but IMO the pogoplug with its stock firmware priced for $18 isn't such a good deal.
Thanks for the clarifications - off I go !