I tapped into my reverse wire on my trailer plug (stock). I have an alpine and it will automatically flip to the camera when in reverse.
As far as upgrades go, alpine (i am a alpine fan) makes a mini amp along with other manufactures that will fit behind the glove box or even down under the cup holder that will allow you to tap into the stock speaker wire. You should see the harness under the cup holder for the amp, pull up a wire diagram and cut/splice the wires needed for the door speakers and BAM you're done (this will take the bose amp out of the picture).
As far as upgrades go, alpine (i am a alpine fan) makes a mini amp along with other manufactures that will fit behind the glove box or even down under the cup holder that will allow you to tap into the stock speaker wire. You should see the harness under the cup holder for the amp, pull up a wire diagram and cut/splice the wires needed for the door speakers and BAM you're done (this will take the bose amp out of the picture).