Input Axis names and axis type (help with joysticks)

Hey all,

The Scripting API/Unity Manual is rubbish here... any help: I want to understand the last three sections of the Input System project settings.

1. (probably the easiest!) How do the three types differ: KeyOrMouseButton, MouseMovement, JoystickAxis?

2. What are the many different Axes about? (X, Y, 3rd Axis (js + mouse), 4th Axis, 5th Axis, ...., 28th Axis)? The documentation only says "Choose the axis of input from the device (joystick, mouse, gamepad, etc.). Defaults to the X-axis.". And this isn't that helpful. My intuition is that for linear floats from -1 to 1, (possibly smoothed-out depending on gravity, snapping, sensitivity, and dead zone), you basically always use X axis - am I right?

3. How do I figure out what joystick my player will use (all?, 1, 2, ..., 16?)?

My use case right now is I'm trying to control two separate Transforms via the left and right joysticks on my Nintendo Switch Pro controller (basically the same shape as Xbox controllers). I would guess that left stick is Joystick1 and right stick is Joystick2. But that doesn't seem to work!