Hi suomynonA,
welcome to BackBox.
You already guessed what you need. What you are trying to do requires port forwarding to the IP address of your attacking machine, generally on port 80 or 443. (Anyways check where web serverr is running).
External port should be 80 or 443 as well, by default, or any other port if you specified it in the url.
But you can read more on about the subject on the web.
Also, we don't think we are going to switch to KDE, becasuse BackBox is focused on lightness and neatness, so we really don't need an heavier DE.
If you want you can always install that, but maybe you'll miss some parts of the original BackBox interface, mainly menus i guess, unless you tweak them. Try if you want and let us know.
Bye.