Note that the Paul McCartney concerts are expected to draw 15,000 people, while other musical groups, like The National and The Postal Service, are expected to draw fewer: 11,000 and 13,000, respectively.
The arena capacity for concerts is 19,000, but usually some seats are not put up for sale, either because the views would be obscured, or the act doesn't have sufficient drawing power.
Note that the calendar does not include arena events that are not open to ticket-buyers, such as the Brooklyn Hospital Foundation Founders Ball, on June 12. I don't know how many other such events are scheduled.
Below, the May event calendar, as issued, which did not include a Nets playoff game on May 4 as well as two university commencements.