Sneakers are fine. Snacks are up to you, I never felt the need, lunch and dinner was provided. I received a Bronco branded water thermos the moment I walked into the place, although I suppose your mileage will vary. They also had plenty of bottled water available.
I don't know about an invite, but I went to the Off Rodeo site and created an account, filled in my info, and had no issues. Attended the Texas site in April, was fun!
I can't answer your question as to why, but I can say that I recently came back from the Off Rodeo in Texas, and we only used Trail Control once to go down a steep hill. The Badlands version I drove didn't have Copilot 360+, and it didn't make any noise that I thought was odd or unusual. The...