Hey Richard!
Looks like you had a great time. It was crowded, but overall I thought the volunteers and organizers did a great job of managing the event. The one main bottleneck was the section across the scree on Devil’s Backbone (where they had setup a rope). They had volunteers with radios directing traffic and working to minimize the “crossing” traffic in that pinch point.
As far as I know, there were no accidents or mishaps. There were of course people who felt the impact of elevation or sun exposure, but nothing related to the crowd.
I heard they had about 1,500 hikers on the mountain. Considering that, it went quite well! Another SoCal hiker reported that they hiked the route on the next day after the Climb for Heroes and didn’t see one trace of trash. That’s awesome!