There is no limit for bleachers and lower tier seats. HOWEVER, the total arena seats limit soft cap is 20k. So essentially, 20k is the limit. However you could sell 20000 bleachers and 0 lower tier seats, or you could sell 0 bleachers and 20000 lower tier seats. << Not exactly right, but I hope it illustrates the point. There is no limit on how many individual seats you sell, but in terms of the overall arena, 20k is the soft cap.
If you have a home game, and the home team forfeits, the home team will still get the attendance.
As long as you start the game with 3 players, the game will continue to the end. Doesn't matter if they all get injured or all of them foul out. Lucky Fans will replace the players and the game will continue.