How many people and how much time would it take to wire a building like the WTC with enough explosives to bring it down?
there was a .mht file from a page that investigated these questions and discussed this very succinctly
Unfortunately, the site was tampered with... by whom, I cannot say.
But it showcased the many witnesses who worked in the building who spoke of extensive unusual activity going.
such as: occupanys on a floor that was supposed to be unoccupied, and OFF LIMITs to all. the elevators didn't even stop on this floor, but those underneath would hear people and thing being moved. changes in regular security routines, including the highly unusual step of removing bom sniffing dogs. bush's cousin being put in charge of security just prior to the event etc., etc.,
What I found most troubling however was that the regular security personnel were replaced temporarily, some informed not to come to work in the days prior, coupled with the removal of the dogs. Every since the 1st attack, those dogs were an integral part of the building security, yet for some reason, authorities deemed it necessary to remove the dogs for a brief period and to give the canine's hunam partners a few days off.

And how would those people go about wiring the explosives so that no one from the public would see them before they went off?
That's a very good question I'd like answered vis-a-vis building 7.
When did they have time to wire that building? the owner admitted it was demo'd,
...when was it wired? ...at noon on Sept 11th... while everyone was rushing around covered in cement dust, or while the firemen was trying to put out the fires?