Your first two photos of the tree did not inspire me. The knobs and the abrupt angle changes at the trunk chops, just not a coherent image to my mind. I just said to myself this is not going to ever turn into much.
BUT, ta da, with the rotten wood removed, that trunk has a whole new character. There is interest there now. Hopefully you can get it to recover, pick up vigor, and start really growing again. If you can put it into a large grow pot, or the ground, and let some escape branches extend out for a couple seasons I think the transformation will be dramatic.
But I would guess you may have been doing bonsai longer than I, so I will ask a question. I was thinking about what caused the rot, and the loss of the branches. The rot could be from water under the old green cut paste, but the loss of branches does sound like heat stress. You mentioned over heating in a greenhouse as the cause of the scorching. I looked at your location. South Carolina, zone 8, why would you ever put the tree in a greenhouse? I winter my maples outdoors here in Zone 5b. I have to mulch them, but they are happier with a sharp cold rest than they are being 'babied' in my old well house which tends to stay above freezing. Too warm in winter (my well house) they come out of dormancy before they can be put out on the benches. Got to keep them good and cold. Not knowing your specific location, I would consider just moving the tree out of the sun and out of the wind for the winter, no real need for temperature protection for winter in zone 8. Top of the bench to under the bench.
And in summer, as you suggested, this may very well be a maple that has to stay in the shade. They are understory trees after all.
But I don't know your situation. I could be completely off base. But it did strike me as odd, to put this tree in a greenhouse.