How do I know where to start and when I've researched enough?

You can look up a statute fine. It is the novel question that unnerves you, the one where you do not know where to begin, or when you have read enough to stop. That uncertainty is not ignorance. It is what every good researcher feels facing genuinely open ground. A novel question has no map, so you make one. Start wide with the broad principle or a secondary source that frames the area, then follow the threads inward toward the specific cases and rules. As for when you have read enough, the honest sign is this: you keep circling back to the same authorities, and new searches stop turning up anything new. That looping is not wasted time. It is the signal you are near the bottom. So begin broad, take notes on what you find, and watch for the point where the sources start repeating. When they do, you are close to done. You will rarely feel perfectly certain, but that settling, where the ground stops shifting, is how you know you have covered it.