GoPro Hero 5 Session camera for long shot (crowd shot) I am asked to shoot noncommercial event, which will last several days. I have my usual camera for close and middle shots (Lumix G6), and I am thinking to by cheap 4K camera for long shots (crowd shots) and cut peaces of them after.

I heard that GoPro Hero 5 Session are capable of recording in 4K, but will it be helpful in this case? Or maybe there is better solution quality/price for long 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.