I'll take one and three together—the agenda-setting and the slots.
The whips in the government have absolutely no power in this at all, so it is in the hands—equivalent to the Standing Order—of the chairman of ways and means, who is the Deputy Speaker. That is not notional, and he exercises the same sort of paternal control that the Speaker exercises over the chamber.
That doesn't mean he's there much of the time. The chairman of ways and means doesn't normally preside in Westminster Hall; other chairs do, from the panel of chairs who do public bill committees, and so on. It is, rather, his baby and not the Speaker's baby; that was the idea 20 years ago.
The actual decision as to how many slots there are is a tricky one, oddly enough. It changes occasionally, but it is decided, ultimately, by the chairman of ways and means; it isn't in the Standing Order.
Currently we have 13 hours. Some longer slots are an hour and a half, and there are some shorter slots, and each day is a mixture of the two. The chairman can vary that, and as the years go by, occasionally they do. We're experimenting now with 60-minute slots, that being the compromise, as you will grasp, between a 30-minute slot and a 90-minute slot.