> Speaking of workspaces, is there no way to only have it show a small rectangle per space in the taskbar instead of a big wide one (I'm using multiple screens)? That's just a useless waste of space.

I missed this one. Yeah, I have the same problem and couldn't fix it but I use a tiling window manager so I didn't need that space for anything else. I've come to appreciate the overview actually and you can drag-and-drop windows between workspaces without having to jump around.

I think the best way to describe Activities is that they filter "what" is available whereas Workspaces filter/select "where" it goes. Spotify automatically chooses my "Background Tasks" Workspace when it opens and it is available on all my Activities. My task manager always shows up in my main workspace but not in my "Gaming" activity. It's a really powerful feature once you understand how it works (eg. notifications from other activities can be muted; separate file and folder views; email accounts hidden in Thunderbird, etc.)

Edit: You could probably get total isolation by using the other TTYs! A fully separate user and different desktop environment even. You just need to use Alt+F{1..9} to cycle between them. For a specialized workstation this could actually be a clean way to handle it.