The Beacon is a tiny theatre... I really doubt it would've held as much as 5000 people. And yes, there were gonna be a lot of executives, but Michael didn't want to perform for 'suits' only, he said he wanted/needed the feedback of his audience being there, so the first few rows were reserved for fans. I don't believe there were any tickets up for general sale, there was an invitation list that you needed to be on and the 'fan' seats were distributed mostly through certain fanclubs and some by radio competitions and personal invite too. There were only a couple of hundred of those seats in all.
And he was definately gonna perform Childhood with Marcel Marceau... Smile was rumored, but not definate, I guess we'll never know if he would've, since Mr. Marceau is not around anymore... RIP. Slash was there for some of the rehearsals too, which caused the rumor that they'd be performing Give in to Me, but we don't know that for sure either. Could've just as well been Black or White...
The health problems that caused Michael to cancel were very serious, life threatening, he was in intensive care at the Beth Israel hospital for three days.