Why would he say he was throwing a party and make people pay. That just coming up with the idea to meet up somewhere and bring diapers.
Yes he suppose to pay for the event, food & drinks till they run out. Then people pay for their selves after stuff is gone.
Generally yea the event is payed for and the guests bring gifts.. That's pretty much a general rule for any party unless everyone's pitching in for beer
Typically, as far as I know, yes. That would be the proper etiquette.