Man, more good questions! Thanks.
Yarrum, this depends on the way your game and group works. I think AW in general and our group in particular is not as focused on maximising effectiveness as on playing an interesting game. Thus having several options has worked really well for us in the past. Players enjoy agonizing over their picks and their ramifications, and their selections have always been something else than what I would have picked. For example, I no longer would be at all surprised if a player preferred to be found out, just so that he can see what kind of shit breaks loose.
Maybe it is also crucial to note that I do not expect this move to be used in our game more than 1 or 2 times, so a key factor is that the move is new to the players and the options entertaining in their own right.
Tod, yes, I assume that the MC already knows who did it. This is aligned with my reading of the AW rules - to make the fiction seem real, as an MC you can mislead but you should also know the who and the why, because this will come up, sooner or later. In practice, for the murders discussed in my earlier reply, I would know who did the deed, and would also know who would be the other likeliest suspects in the minds of the players (and the mob).
The amount, exactness and completeness of the actual clues will depend on the options the player picks, and I would not prepare them in advance. As usual for our game, I will lean heavily on the players to provide details, and use those details to point to various suspects as needed.
Like: "You remember that Hothouse had that unpleasant habit - what was it?" Player: "Er, constantly chewing a piece of cloth, yeah, hanging half out of her mouth, all disgusting, with saliva dripping wherever she went." Me: "Ok, right, so... When you put your hand under the desk, that's what you feel - a wad of cloth, all moist and clammy."