1) Your assumptions about the rear signals are correct.
2) The special washer is just a flat piece of metal that holds down the wire coming out of the kick stand switch. You don't need one.
3) Either JB weld it or get a new holder. I've done both. The JB weld didn't hold up, so I ordered a brand new mirror/lever holder.
4) I don't know. It looks like a regular o-ring? I've got the older style carb so I'm not familiar with the new style.
5) That sounds fine to me. You can try and mess with the screw. If yours starts in that weather, I wouldn't mess with it too much.