I have attended the last 3 games that the Bills have played here in KC (1 win, 2 losses). The tailgating is excellent with a lot of great barbecue. The Chiefs fans will give you a hard time if your wear your Bills jersey for the most part it will be good-natured fun.
There will be quite a few Bills fans in attendance, but most Bills fans that I know get tickets from Chief season-ticket holders. So, I don't think we will have a seating section but will probably get together to tailgate.