Bulfer says it is not less than 59%N2 to allow for IDG operation. This would either mean to ensure adequate inflight IDG operation of generator or to allow disconnect to take place if needed.
Regard it as a circuit. I believe when you have difficulty in operating the automatics adequately when a lot is going on, simply say 'I have control, my throttles', disconnect everything and pull throttles back to a sensible power early. Fly it as you would a normal circuit. you can re-engage automatics at your leisure, but the important thing is not to blast through 1500' with GA power and too much flap while you are wrestling with MCP modes!