The number of attendees in KC was the total attendance over the three days. They weren't getting 300k per day in KC; it wasn't much more than 100k per day which isn't much more than GB has on an average game day. Yes, lots flew in, but the majority were local. And they won't have lawn seating like KC; if it's in the stadium, they'll only be able to sell ~60k seats at max because the stage will block the view of at least 20% of the seats.
Unlike other large cities, the hotel rooms in GB/Fox Valley/Door County will be empty that time of year. No competition from conventions, business travelers, no holidays or special times of year (such as fall in Door County, summer on the lakes, etc.). And on game day, many people choose to stay 50+ miles away because every hotel within 30 miles of Lambeau has a 3-night minimum on game day weekends.
It's really not going to be much different than an average game day, if not smaller.