3. Where are the Limits to Player Authority over Narrative in 5e?
The more interesting question is- what about narrative control? What amount of control does the Player have over the narrative and the environment of the world? I will start by recounting an example I saw where this issue caused a table conflict, and then delve into why this might be important-
Briefly, an individual was trying to DM for the first time, and was running a "canned" adventure. One of the Players ("Player A") used a very heavy "narrative" approach to the game. At a certain point, there was an encounter with a guard. Player A engaged the DM in dialogue, and seized narrative control by creating fiction that had not previously exists (that Player A's character had a relative that the guard knew, that the relative was sick, etc.). Again, this was not a bluff, nor part of the prior knowledge of the world- just extemporaneously created fiction. Which caused the DM to freeze up, because the DM didn't know how to deal with it. And led some of the other Players to question Player A - as they felt Player A was trying to "game" the system.
Personally, I don't think anyone did anything wrong there. A more experienced DM who did not want to cede narrative control could easily have parried Player A ("Oh, you must have mistaken me for the other Guard. No, I don't know you.") until the table could discuss it. But it illuminates the issue of mismatched expectations regarding the amount of control Players have over narrative, and why it's important to have that division of authority ironed out. Importantly, it also illustrated the usual point of conflict that might occur-