Definitely more than 100k on the march, I've seen figures as high as 3 mill, which looks like an over estimate, I could imagine 500k from the pictures and videos I've seen.
Been very impressed with it overall, thought today we seemed a bit off with stray passes and some poor decision making etc, but we should have still been way out of sight.
I wouldn't necessarily say it needs to be a pro or specialist trained. I've shot guns on my travels to other countries and you get fairly accurate fairly quickly. A few afternoons at the range would make that shot.