Hi XCali,
thank you Yes, patience is the key. And time, I guess
I've found some very helpful tutorials, also on other websites, and with them I was able to already generate six different maps. One of them is this: http://fs5.directupload.net/images/170728/9vntv9er.png
Well, it's not entirely the result from the ideas in my head because atm I'm working with nebula photographs turning them into maps but for the moment this will do the job until I'm more experienced with GIMP and Wilbur.