Well, the minimum set would be if we had developed all the capabilities required to walk on the moon, but we had also secretly developed capabilities to fake the moon landing with special effects, and for some reason decided to fake the landings even though we had all the capabilities to perform them. That set would included the astronauts for all the landing missions, all the scientists who examined the moon rocks, the special effects technicians, and whatever shadowy people were coordinating all these fake activities and assiduously duping the many thousands of others who would be working closely with the conspirators and would know enough about the mission to spot things not adding up. So definitely in the hundreds if not low thousands of individuals. Because the radio signals from the moon missions were picked up by the Soviets and others who would not have been in on the conspiracy, the technology to fake the moon mission would probably have to be more advanced-- and certainly have to be far more secret-- than the technology to actually perform the mission.
If the moon landing were faked because the capabilities that were developed to perform the moon landings were also faked (which is the only non-absurd reason to fake them), then you are talking many thousands of additional people who developed and documented those capabilities who also have to be in on the conspiracy.
