In order
1.1. I've had that exact same issue on the Ubiquity (or Ubuntu) installer with no idea how to fix it, it seems to be an Orca and general Linux issue unless I'm missing something here
2. It should, I think be in the key mapping settings. The oft-used but not default win+alt+S isn't mapped to it, though it isn't mapped to it for a lot of distros either
3. Yes, go back to the desktop and:
1. a) Hit control alt delete, it should bring up the power options
b) If using Mate,hit alt F1 and hit up to jump to the end of the menu, you'll find logout and shut down
If using Budgie, control alt delete works
If using Gnome, hit windows key and type power, go to power off and that'll bring up the power options
Warning: Grumpy post above
Also on Linux natively
Jace's EA PGA Tour guide for blind golfers