p.s. But if like stay horizontal, with the 4"x4"x4" jammed to the back of the stove, with the 4"x4"x4" combustion space in front of that, with a baffle above so that air flow in through the open door and combustion gasses pass forward under the baffle and then up and over the baffle and back across the top of the baffle and under your cooking surface when not covered, and then up the stovepipe. In such a conventional configuration, even though it is horizontal, it should radiate most heat out through the door while it is open, because you can see the wall of flame as it burns through the batch of wood. Also, as ash builds up it can fall and be scraped away.
So maybe horizontal is better.
p.p.s I like your design with the stove simply cantilevered off the stovepipe. The stove should be light enough for this, even when loaded and with a pot on top. Not sure of best diameter and height for a stovepipe, when minimizing weight. I like the idea of switching to aluminum tubing after a certain distance from the combustion zone. Perhaps the entire stovepipe could be a single aluminum tube, doubling as the tentpole, and hiking staff. As long as the baffling and insulating was done right, and the stove was loaded and operated right, I can't see that being a problem. You could then go with a diameter that is just comfortable as a hiking pole without being too big, like 1-1/4" maybe, or 1" if you could make the stove small enough.