How do you know when you’ve interviewed enough people? When I realize I know more than the people I’m interviewing. When they start interviewing me about the story—when I’m perceived as the “expert”—I know I’ve talked to enough people.
So you write section after section, day after day, until you finish? No, I go back over what I’ve written. Almost everything can be improved the next day. Sometimes, when I get to those sections that seem like boilerplate, I’ll deliberately write poorly and quickly, just to force myself to make progress.
Describe your writing voice. I try to be companionable and firm. Sure, friendly, honest.