So now that this summary is complete (is fifty pages a summary?) I now have a chance to go back through and really hone the story.
First up: Kylo being the vessel for the Sith was actually a later addition to the plot, so the first act would really need to give more substantial Sith haunting. I imagine that Kylo will continue to grow in power as the hold of the Sith becomes stronger, to the point where he feels like he can stop a Star Destroyer falling out of the sky. Rey will need to grow in power in Act 1 as well to match Kylo.
Second: The more I think about it, the more I feel that giving Rey any backstory of importance is fundamentally at odds with what makes her character compelling. So Maz’s lightsaber story will need to be cut or substantially changed.
Thrid: The final act is, I will admit, a bit of a mess. In attempting to give every character a meaningful conclusion the story jumps around too much and Rey is almost forgotten. I will need to give more thought to streamlining the final battle.
Those are my first thoughts at a second draft anyway.