You pretty much have your questions answered here but just a few afterthoughts; you may want to make the final tightening of the seat clamp higher on the post than in the rear view photo. There is evidence of the seat material bottoming out on the bolt head once it is compressed when sat upon. This will create an eventual wear spot on the seat fabric and may be uncomfortable on your butt.
Also, it is possible that a conventional split seat binder frame was once used on prior productions but for some reason they opted for a quill post here. Of course all of the hanger/mounting suggestions remain very valid ideas.