There are extension boxes that add depth to the existing box.
Technically no, as long as you can avoid touching the wires on the outlet or switch...
It's a multiple of eight per strip, so there are actually 200 spacers in each 25-pack. Besides, wouldn't you need an odd number for a 3-way switch? ;-)
Yes, they can.
Yes, easy way to shim receptacle to a receptacle box a little too deep inside wall because add paneling or tile . Receptacle box should have been out to account for additional wall panel, tile thickness.
You can stack as many together as you need for the desired thickness.
It should be if the outlet is mounted properly