This space for rent!
Painting all these miniatures is starting to crimp my time...
No, per p. 8, "Assign Agent", Rulebook: "You cannot place an Agent on an action space that contains another Agent (yours or another player's) or on Buildings that are not yet in play."
Can more than one player's agent be assigned to a building that is out on the board?
So a building may have 2/3/4 agents and the owner gets a benefit each time on that turn that an agent lands there?The only way an action space of a building can have multiple agents assigned to it is if the assigning player has completed the Magister's Orb Plot Quest and the action space has an opponent's agent on it.
If multiple agents can go to the same building, can one player send multiple agents to that same building?
The Owner "gains the stated benefit when any other player assigns an Agent to that Building" (p. 7, "Reading a Building", Rulebook). Thus, another player assigning an extra agent via Magister's Orb (or a "virtual" extra one, via Bribe Agent or the Zoarstar; Rodney's clarification) would again yield the benefit for the owner.