Regarding the leads, I know it's a little late but I left only a small amount out the right side for the passenger and the riders lead came out by the lower left part of the front seat.
I don't have any noise in the autocom, even with the GPS on. However, when I turn on the J&M CB there is engine noise present. I have been told that the audio on the phone is a bit noisy when the engine is running. Since the wires pass right my the left hand ignition coil, I suspect it is the culprit. Don't know any way around it.
With a 20 ma draw when the headsets are unpluged, the battery drain will be minimal.
As for hearing your self when you are "singing" along or just talking to yourself, with the ambient noise sensor set right, at speed the vox is made a little higher and you do have to raise your voice a little to trigger the VOX.
On my recent trip, I was using Push to talk in the CB and I wish I had wired in a switch to allow VOX operation. Sometimes I make a transmission and forget to press the switch, especially when I was answering someone. It's like having a passenger talk to you. Your natural response is to just answer the question.