At a minimum, in the GMs mind or notes. Just odds of existence are enough; "2-in-6, cook" for example.
No. Something like "in each room, roll 2-in-6 for servants; if servants, roll 2d10" would be better, imo.
I feel like these two sentences conflict to some extent. In the situation as described, the cook would be something in my mind as a possible complication or encounter. I wouldn't have odds like you describe because I would rely on a different method to determine when and how she shows up.
Yes for the watchman because they play a significant role in the break in. No for every single NPC. If the existence of NPC is at a prime adventure site, better to have more detail (again, a table or odds is enough). If the players decide to break in to a location that had not been fleshed out, make some quick decisions before the break in.
Well, we don't know if the watchmen will become involved or not when the situation begins. There's a possibility, sure.
I'm asking what you think is sufficient to run your game. How much detai about the estate do you need?
This very much depends on the game in question. I would approach it very differently depending on the game.
Assuming 5e or a similar set up, the main thing to know is what interest the players have here. If the goal is to steal a map, then that's the most important thing for me. Then I go with what makes sense based on what's been established already in the game. If we know the owner of the manor, and if his importance or status in society has been established and so on. Obviously, we know he's affluent... but are we talking like a minor noble, or an uber-rich noble? Those things may matter. Also, what family connections have been established? Is he married? Do they have children? Does he have household members who are not blood relations?
These things may help determine who is within. If they've not been established, then I'll consider them as things progress, and decide as needed. If these kinds of things haven't been established already, then I'd make a decision. For instance, given the importance of marriage and heirs in medievalish cultures, I'd assume a spouse and some children. Would there also be someone potentially dangerous? A personal guard or right-hand man type? That seems to make sense, and would create for a possible danger to the PCs. I'm also picturing a pair of hounds that serve as a form of security. One sleeps at the foot of the stairs leading up to the family's quarters, and the other sleeps in the nursery with the children.
That's about as detailed as I'd need to be to get started.
I think if the conclusion here is "people dislike narrative games for well founded reasons about what they get out of play" rather than "D&D gamers are reflexively conservative in the mechanics they use and that is exhausting", I'd be satisfied.
I think there have been plenty examples of both in this thread. And just to point out, Fail Forward may be part of some specific games, but it can also be used in trad games.
I think that, for me, where the exhausting bit comes from is that just the very idea of Fail Forward being used in a game like D&D. I think it's perfectly fine to not like Narrativist games... but when we talk about a method available to GMs to use, even in trad play, the resistance to it is kind of bonkers. The twisting that happens to render examples non-sensical is remarkable.
Like, the example of the cook and the kitchen... if the cook being introduced as a complication on a failed roll doesn't work for you, then you just don't do that. You can instead have any number of other things happen... whatever you think makes sense for the situation. If your prep indicated a hound in the house like I mentioned above, perhaps the thief hears a low growl on the other side of the door. Perhaps a neighbor notices the thief at the door and calls out. Perhaps the town guard happens to wander by.
The idea is just to not have "nothing happen". That's all. Is that really a bad idea? And, let's say that you decide that the best thing that could happen in the case of the thief at the door is that the door remains locked and he has to figure something else out? Okay, fine... go ahead and do that! That just means that you didn't use Fail Forward in this instance. It doesn't mean you never could or should.
The outright rejection of the idea is the exhausting bit. Unless everyone here truly believes that the only thing that should ever happen on a failed roll is "nothing happens"... which I highly doubt.