Aloha to whoever reads this post.
I will explain to you how i installed the latest version of Windows 10 November edition on my external hard drive so it can be used for a Macbook Pro 15". It is advised to have a mouse and keyboard at hand before starting the installation.
I found and used the following tutorials for this adventure:
I followed the steps of the tutorial from Chris K which was posted at the article from Sven Kirsime and it worked marvellous. The last steps i didn't had to undertake so let me walk you through it.
I followed the tutorial till the step ten and walked into my first problem. On my mac i have 10 virtual desktops for working related purposes which created some confusion around the virtualBox steps. Every time i switched from one desktop to another for example for reading the tutorial, the running instance of virtualBox would abort and close. Be aware that you should not switch the desktops while installing windows. I also had to eject the external HDD every time i wanted to start up the virtualBox instance since it would automatically connect and then throw a "medium is busy" error.
After the installation was completed i saw the 10 seconds till restart window and closed the virtualBox instance as described in the tutorial. In the comment from Chris K we are at step: "Restart Your Mac and Boot from the External Windows Drive".
I rebooted my mac and pressed the option key so i could choose the external hard drive. I was not prompted with the 'EFI' screen and windows started installing itself. After a while it restarted again into macOS. I just forgot to press option. You then just restart again and boot into windows two more times since the installation needs some restarts. I had to plugin a mouse and use the virtual-keyboard since i had no keyboard at hand in the moment. The installation worked and after i logged into my fresh windows installation i could install the drivers from bootcamp. I installed the most of them from the folders Apple, AMD and WindowsPE.
I could not get the keyboard or trackpad from my mac to work so i just use the external mouse and keyboard instead.
Well thats it, quite unproblematic, now that i am travelling for three weeks i have a working running windows on my external hard drive.