Hello,
take a look into your routers configuration interface. Here you should have 3 entries for port forwarding:
port 80 (http), port 443 (https) and port 4125 (Remote Desktop Proxy) all redirected to the correct internal IP address of your server.
Also update the firmware of your router to the latest available.
Can you access your WHS internally, i.e. with
https://server ? This will bring up a certificate warning first, which you can ignore, but would show at least, that IIS is configured properly.
Best greetings from Germany
Olaf