1) If this isn't set up by default on 6.0Beta2, check the forum for a proftpd contributed RPM that should lock the user into their home directory (IE, prevent directory enumeration). I can't be much help with 6.0Beta2; I've not used it yet. Not sure if they even use proftpd.
2) "Post Room" - Create an Ibay called Post Room, create a symbolic link in each users directory to link to the IBAY folder. Create the symlink relative to the FTP links.
3) Same as #2, however, adjust IBAY permissions to only allow read for students and read/write for teachers.
For help on creating a symbolic link, try "man ln"