I've deleted loops and now arrived at 813mb in GarageBand,
I guess that will be ok as I can't find anything else after searching "Application Support" and I can't find an "Audio".
I also can't get the -
- With that Finder window as the front window, press the key combination ⌘J to bring up the View options.
- In the View options panel enable ’Show Library Folder’. That will make your user library folder visible in your Home folder, if it is still hidden.
to work.

So things seem be running better now.
Except that I'm now having problems with Safari. It won't quit unless I use "Force Quit" all I get is the colour wheel.
Looking through the forum I see other fairly old posts/threads referring to this.
However I wonder if you had any ideas?
As an idea I've just completely re-installed Sierra V 10.12.3 from the App Store, but that didn't change the problem.
The screen shot above was taken after I'd downloaded Safari.