I believe both of these are available through Pypi, which you access via pip.  You have it if you're using Python 2.7.9.  If you don't have Pip, then go read up on how to instal it because you want it anyway.  Once you have it, pip install packagename.
Pybox2d may not be available through that method, in which case you need to download it.  I do not know where; my physics library of choice is ODE, for now.
Pybox2d is a port of the C++ code to Python as I recall and, consequently, you shouldn't need anything else.  I cannot walk you through using it, I'm afraid; I use only Ode.  For what it's worth, Ode is more complicated in a lot of ways.

The answer is yes.  You can use them together.  But you should be aware that you're asking if you can use your house with your car-they have no relation whatsoever.
I do not use Ode for physics because Ode is a 3D physics library and most audiogames need a 2d environment, usually involving tiles.  Pybox2d might be better if you're going to try physics simulation.  The killer feature of Ode is that you can use the Geoms without using the physics part.  This lets you apply velocities and stuff yourself in a "sane" way, but use Ode for fast collision detection of complicated scenes.  I do not believe Box2d can do this for you.
I learned  it by downloading and installing the Ode bindings from here, reading the C documentation, and using dir on the module to find the things I needed.  Ode is the kind of thing where a Python-specific tutorial isn't going to help you much-if you're a good enough programmer to make use of it, the C documentation is good enough (in all honesty, the C documentation for Ode is amazingly amazing, but I digress).  The hard part of Ode is not the API, it is understanding the concepts.  Spheres and boxes are easy, and don't need much but the constructor and setPosition for good use; other objects are harder and may involve transformation matrices depending on what you are trying to do.  The one notable feature of Ode and the reason you probably want it in the first place is raycasting, i.e. asking "does this ray hit anything?"  You can also do this without transformation matrices, as the ray object provides a function that takes the place of such manipulations.
The one thing you should never do in Ode is set the z axis to 0.  Doing this causes weirdness; to get around it, make all objects 1 unit high.
I can post a snippet, but it's part of an entity component system.  This means that it's very far from what you're used to.  It also handles multiple environments and a whole bunch of other stuff and is like 100 lines.  It's also a bit horrible at the moment, though I'm not sure there's a better way to write it.  I'm afraid I don't have a stand-alone example of using Ode, though some Googling can find you one in all likelihood.

I have no idea, but probably.  If it has pan, then yes.  I'm using my own custom sound engine, etc.  The only thing you might want and might not have is pitch bending, but again I'm not using it for sound so can't comment.

Nothing can simulate a 2d environment where something is behind you with something that's not pan, save for a very few games in BGT, Libaudioverse, OpebnALSoft, and some commercial packages.  It is what Swamp is doing, what Shades of Doom does now that Directx sucks beyond all telling for audio, etc.  It's not so much about can or should, it's more about not having much else in anything that you can use.