Question: What was the reason that God told Bruce he couldn't interfere with free will?
Answer: Because it would no longer be "free will." Humans were given the ability to make their own choices. If God began controlling everyone's will and actions, they'd no longer do anything based on their conscience. Making the right choice can be more difficult and challenging than doing the easy or wrong thing. It's a matter of an individual making the decisions.
Question: Aside from it being a funny scene, is there any reason why the people at the news station would keep the feed on Bruce during his tirade at Niagara Falls instead of switching back to the studio?
Answer: I think they are all just stunned about what they are seeing, and perhaps a little curious.
Question: Is there supposed to be any significance to the elevator being out of order in the building Bruce is sent to?
Answer: Also, Bruce needed to learn a little humility.
God recognizes that Bruce is expecting things he hasn't earned and is attempting to teach him about the importance of hard work and earning things. Bruce has to climb the stairs (harder than taking the stairs) and God asks for his help mopping a very large floor (hard, but satisfying work).
Answer: It's just the idea that using the stairs is better for your health, so God forces him to use it.
Answer: They most likely called him and invited him back in to get the scoop. Before another network gets him.
lionhead