World Trade Center
Answer: I would probably ask the 5,000 people beforehand to bring in an artifact about the issue they want to discuss, and bring it to that event. Then when people discuss their issue at the table, and vote, everyone is on the same page.
Then I would probably collect their artifacts, and display them on a wall or inspiration board, whether part of an exhibition or not. That way, people can assume that their time and thoughts were considered.
I was impressed with this exhibition at the Center For Architecture. These two walls display numerous articles about the design and construction of what the new Freedom Tower.