I can join your server now. So it seems that the basic configuration seems good. Don't know why it works suddenly - yesterday it didnt work for me. There is no registration needed.
We didnt write more about the firewall rules, because windows proposes the rules automatically.
So if you have the error with the "No record of this Game Server on the Assist Master Server, Cannot Authorise, Please try joining a different server." it sounds to be the NAT Loopback error - because we can join from WAN.
Try to find out, if your router / firewall supports this feature. Maybe it's called DMZ Server or something like that. Check the whole configuration possibility of your device, whith the manual.
If there is no way to turn this on, you have to buy a new device or you'll never can join your own server