On OSX - Command+Tab for switching to the next tab and Command+Shift+Tab for switching to the previous tab in the script editor will not work since those are reserved by the operating system for switching apps.
Try holding the Fn key, or if that doesn’t work remap the key combinations in Renoise Preferences.
The scripting editor/terminal shortcuts are not availlable for remapping. This is mentioned also in the keyboard issues megathread here.
Wow that’s a good list. Thanks for taking the time to write about a lot of the things that had been bothering me (but that I was too lazy to write about 
~r