WM in NOT a full FTP server. It can accept a transmission and pass it to a service, as specified by the CD command. Users are defined on the WM user screen and you can control which which services they can invoke.
But, WM does not have the core file managment functionality that you find in an real FTP server. Most of the features you mention could to be implemented as flow services, but there would be all sorts of issues.
You need a real FTP server. There are many inexpensive implementations available. The best choice would depend on your specific needs. I use the Serv-U server. (www.serv-U.com)
It will be far easier to put in a real server and, if needed, access it from WM with the ftp client commands.
#webmethods-Protocol-and-Transport#webMethods#Integration-Server-and-ESB