Where to put users home directories on Mac MIni Server?

I've got a setup question on a recently purchased Mac Mini Server: I bought the server as a family server - a place everyone can store their files centrally, store multiple iPhoto libraries (100+ Gb?), iTunes libraries plus FLAC collections, a recipe wiki, family calendar and address book, plus a centralized scanning repository to get rid of mountains of paper. I figured that would require a lot of storage so I bought the Promise 3 TB raid (5). I set the two internal MacMini 500 Gb drives as mirrored Raid 1, so the system drive now has 500 Gb. Should I put the users' home directories on the 500 Gb system drive - there's still a lot of space on it, and I don't see adding many apps to the server - certainly not 400 Gbs worth. But when the users need more space, can they somehow expand onto the Promise RAID? Or would I need to set up a second sharepoint for them, which would appear as another attached drive on their desktop? Or should I just start them right off on the attached Promise RAID, which has so much room and will be easier to enlarge?