not sure I follow. Regarding your original requestion, to obtain your WAN IP, you would need to say go to a site which looks up your IP then parse the page in some way or use a web service of some sort.
in regards to configuring your router or setting up your computer for FTP, im afraid this goes beyond the scope of the development forums and becomes more of an admin/management type question :-)
obviously you need user credentials set up so no one can just log in without permission/request. you also implement a firewall solution to protect hackers as well as anti virus software.
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