filipp.name

1) To allow only FTP access to a share (AFP/FTP/SMB):

$ sharing -e sharename -s 010

2) All the configuration files are in /Library/FTPServer/Configuration
3) "man ftpaccess" had some useful info on the different chrootType values:

chroot_type standard | homedir | restricted

            Sets  the type of restricted environment the user is under when he

            logs on.  standard Allows users to  access  the  ftp  root,  their

            homedir,  and  sharepoints.   homedir  Allows  users to access the

            their homedir and  sharepoints.   restricted  restricts  users  to

            their own home directory.

and they all work with serveradmin:

$ serveradmin settings ftp:chrootType = "HOMEDIR"