How do I setup management keys/escape for Steam Big Picture + Big Box?

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I am current setting up a solution where I use Steam Link + Big Box on Steam so I can remotely access my arcade from anywhere with just my Steam Link hardware + controllers. I have the whole thing setup and working locally but I'm struggling to configure the controllers to access things like:

1. How do I exit games I've launched via Big Box in any of the emulators I've got (MAME, Retroarch, PCSX2, etc)?
2. How do I access the in-game MAME settings (Tab key on PC) with a controller?
   1. I guess similarly for any of my other emus setup.
3. How do I disable the Windows Gamebar it seems I can pull up on my generic controller via one of its buttons? (I want to idiot-proof it)