What to expect when the named users => max.named.users ?

Hi

In the metrics of our app I see that the named users are reaching -at peak timess- our max named users of 100 named users.

1 - So I am wondering what i should expect when the named users reached 100 (system notifications)?

2 - And what will/could happen when someone tries to make the 101st account (will the app crash, any other possible effects for the 100 concurring users)?

3 - Best practices to capture those peak times?