Unfortunately, here I’m bounded to the limits of Godot 3.x. It’s not possible to handle multiple “real” windows. Otherwise, I would like to have a more “docking”-solution with separated windows.
I also have a 4K monitor, but I work only at 150 %, so maybe that’s the reason it' all a bit big ^^.
Yes, the problem with the preview is a known bug, but it’s just the preview so I didn’t give it high priority. Because it worked and I needed to fix a lot of other bugs first :).