That sounds like a good idea to me, keeping Vader within the Empire and taking things down from the inside. Perhaps the Mustafar confrontation could be Luke surrendering to him?
I’m not sure you need to kill off a big-name hero. ROTJ was satisfying without it. Maybe include Akbar in III and kill him in IV? Take inspiration from the story of Admiral Yi, with him dying on the bridge and his subordinates commanding the battle for him.