Quick tip for Time Machine backups: Mac OS X Server ("Server.app" these days) can setup a quota for Time Machine backups that is specific per-machine (rather than per-user). This trick works on any share, actually, since it's a root-owned property list in the share directory. You'll want Mavericks or later as a client for this to work, but to set it up cd into the root of the Time Machine share and create the plist with (for a 500GB example):

/usr/libexec/PlistBuddy -c 'Set :GlobalQuota 500000000000' .com.apple.TimeMachine.quota.plist

On the server, make that owned by root:wheel and chmod 644 et voila! You have quotas. No need for "real" quotas, LVM, or other fun. Works over SMB and AFP.