I’m usually using ssh to do things like this, had to search the internet for how/why in this case though, due to the fact that wordpress rewrites your adress(?).
From putty create a port forward under the SSH/Tunnels tab. Set source port (your remote pc) ’80’, and destination (your raspberry) to ‘localhost:80’ . (not the ”’…).
Make sure your router forwards port 22 (ssh) to your raspberry and it should work. I guess all your web traffic would go through your raspberry with this setup, which is why I would normally use port 8080 for the source, but wordpress rewrites that to 80 anyways.
As for your WAN ip, just setup a script on your raspberry to email the WAN everytime it changes. Not so often it does though, after the worlds government decided to track everything ISPs try to keep adresses as static as possible. Here is a link to such a script (my own). https://dephiox.blogspot.se/2016/01/obtaining-external-wan-ip-address-from.html
