I like your plans, continual improvement.
It is spring or early summer in your area, I would cut at the yellow line as soon as possible, your plan will work. Of course, look at the health of the tree, before you cut, wait if you think it needs to wait, but from the photo it looks like it could handle the cut. Your plan is a good one to my eye. Wire the other branches this season, before they get too stiff to move easily.
One caveat, I did not go back and re-read the whole thread, so I have no idea how long this tree has been in development. My thought is, you have a lot of trunk, only a small part of it is alive, and not a whole lot of foliage. To survive long term as bonsai, trees need to grow. If it were mine I would have a plan where perhaps 2 consecutive years, in every 5 year cycle I would let it grow out, extend and go somewhat wild. I'm not saying this is mandatory, just a thought, to consider. Perhaps do your cut, to see if it back buds, wire to shape. Show it at your local show this year & or next, then give it a could years to go wild. Then bring it back in to show shape. But I am not a bougie grower, my single bougie is a small shohin, and it needs this sort of ''let it go wild'' every not and then. I'm growing it under lights most of the year, so it is not in ideal conditions, which is perhaps why I think they need a grow out year or two. So based on your own observations, go with or ignore my thought. Health of tree comes first once a tree has reached the quality level this one has. Yours is quite nice.
I did not appreciate the scale of this tree until I saw your hand with it, it is quite a bit bigger than a shohin. Nice.
