Here are the door disassembly PDFs
For the multimedia system, you won't be able to replace it on your own. Because of how they are linked to the vehicle and CAN systems, modifying or replacing it will brick the head unit and some of the non-critical vehicle functions unless you have some of the specialty dealer software to correct it.
If you
KNOW you're going to want the bigger head unit, I would highly recommend getting a trim level with it. It ends up being cheaper to get the higher trim than it is to source/buy all of the necessary parts to support the screen size upgrade.
Dodge Avenger Workshop and Service Manual 2008 2010 PDF