I have a similar situation with my Japanese schefflera, but not quite as drastic. Like you, I want it to be shorter and more dense. I understand schefflera is one of the easiest to re-root. Since my tree is outdoors on the porch, I am going to wait til warmer weather, cut it down to the size I want (or shorter) and replant the cuttings in the very same pot. 3-4 of them I am going to try to Bonsai in smaller pots. Water and fertilize as usual. Have you thought about moving your newly trimmed-back plant to a window where it will get proper light?
