as i said, the drives doesn't need to be formatted in a speciffic type of format when you have them as a media shared on a network, afik you can use whatever type to share since when you are in a network ,the acces is not done directly to the drive, it goes first to the pc using the required protocol but i could be wrong
about sharing space for linux on one hard disk and the rest for mac, i personally would only have a ntfs or a ext4 partition shared for everyone but this depends on the way you want to share(what for who and how much for each one)
samba is the protocol to share files on a microsoft network(useful to add a linux machine to a windows network without going crazy), since you don't have windows machines on your network(at least what i understand) samba sounds like a extra step, unnecesary
i only have done this by using samba so no idea how it is done on anything else, set up the mac network and share resources with the linux machine or if all the machines will just access one resource(no access between mac and linux, just each machine to the disks/shared resources)
if you are using one of those beautiful nas like this one( you mention a enclosure for 6 drives so i assume a big nas unit)
http://www.compsource.com/ttechnote.asp?part_no=GS3215&vid=181&src=PWthose uses two ways to be configured, from a ip opened by using a web browser or from a native windows or mac app that allows to create partitions, arrays, types of partitions, shared resources and similar stuff, this will limit you to what partition types will be created and how the resource will be accessed