He'll start by deciding who the protagonist is, and he'll have to cut the whole film with that in mind. It may be Rey or FN again, or possibly someone else. If he knows the beginning and ending it will be easier for him.

If Kylo and Hux are double agents (best theory IMO), Episode VIII might screenwipe to their perspective after the opening, introducing an associate like Tom Hardy, and show us a dark side trio of friends reacting to the loss of the Hosnian system. Joy or regret or something inbetween. They'll establish why Kylo cracked up and if other characters within the Order are feeling the same spiritual pressure. Del Toro will be introduced. External politics. They'll cut back to Luke and Rey's movements. Lando. Dern. Hardy could persuade FN to be a Stormtrooper again which would rupture the Resistance, and one member of the dark side trio might gradually change sides or be rooted out...

At any rate, one of the villains returns to Luke and crosses Rey. Luke definitely won't star though, he'll probably be an unpredictable Harry Lime figure. 30-45 min. screntime max?