What Belongs in a Quickstart Guide

Based on some of the other comments, I started to write a comment here earlier speculating that maybe there should be two versions, one for the GM and one for the players. But that doesn't actually make sense... instead, just have a quick-reference section for essential rules that's primarily targeted toward players, and a story module that's primarily targeted toward the GM.

Why not present the rules through the context of a story module? Well, that's very appealing, but the players should be able to have eyes on the core rules themselves so they can look things up and learn on their own, rather than depending on the GM for all answers and to be the source of truth. It's better for learning to get the information through multiple channels anyway, and it takes a burden off the already-busy GM. But the players can't have eyes on the story module, or it would ruin the surprise.

So, you have two parts: a simple rules reference section for players (which the GM should also already know), and a story module that the GM can follow which is deliberately designed so as to introduce players to rules one at a time.