Well, a fresh morning (at least in the region I live) and a fresh try, right?
It worked - like pana states, the wp lingo is confusing or confusing me...
First off, my bike did have a problem, it was not me misusing the controls :-)
Having that said...
1+2: I think it is rather strange, the default top nav is not shown until I create a (what I see as) a custom menu and when I select nothing in the dropdown, it still shows. I think it would be far more logical to have a ´show top nav yes/no´ option in the dashboard...
3: see above.
4: Of course it doesn´t move anything, there is however the difference between human lingo when explaining what one tries to accomplish and strict ´programmer´s lingo´
5: True, however... because I know that in the future I might want to add more items to the custom menu I chose to use that feature instead of the Pages widget.
Any way, thanks for your support and patience!