The Vice-Chairman of the committee that heard Butler’s testimony was later revealed to be a Soviet agent (probably more for the money than out of ideological conviction, though).
There was definitely an interest on the left in building the story up to be a major indictment of capitalism and the millionaire class.
Interestingly, some of the closed door testimony has never been made public — or presumably, found. Make of that what you will.
Yes, you can see how they would try to exploit that. They were always trying to raise awareness of the evils of capitalism. The "Monopoly" game was invented by a couple of communists with the intent to show people how evil capitalists were. Amusingly enough, people loved the game and didn't get the larger message they were trying to sell.
Interestingly, some of the closed door testimony has never been made public — or presumably, found. Make of that what you will.
Probably inflammatory and/or implicating powerful men or businesses. A lot of major US companies were doing business with the Nazis back in the 1930s. Probably wouldn't want any of that to get out if it could be helped.
A coup? Probably talk, but I very greatly doubt anyone seriously thought of doing it. Roosevelt was a very hated man by a lot of businessmen of that era.