GoPro Hero 5 Session camera for long shot (crowd shot)
Yes, useful for wide crowd shots.
Yes, you can crop down/scale up 1080p selections from the 4K to simulate additional camera angles.

Consider using the gopro app or a wifi remote to stop/start the gopro so you don't have to physically access the device while monitoring your main camera(s).

Not sure how long the event will run for but you might want to look at an external USB power source too.