Proceeding with the steps as mentioned on a fresh Windows 10 install, I tried at each step if FS9 would start.
After the initial install from CD in a suitable folder, it would not, not even in compatibility mode and/or run as adminstrator. Simply nothing happened.
After applying the FS9.1 update, it did, but with graphics problems: the settings windows window was unstable, only partly displaying its content, and the actual sim window just black.
Both that phenomenon and the cure for it can be found in the topic Fs9 under win10, also in this forum. I downloaded (beware to decline the unwanted stuff) and installed the DirectX June 2010 redistributable et violà: there is FS9 up and running. Thanks Crimar!
Full screen works fine for me btw, without any specific tweaks so far for that. I am however someone who tweaks his OS beforehand, and I always disable a number of 'handy' automatic functions and eye candy that I don't like. The GTX1070ti video beast may help as well.
Many thanks again, Tom, for providing another 'standard work' in helping with FS9 setup!
Edit - P.S.: I rolled back the compatibility mode and Run as admin options before applying the FS9.1 update.