Just for clarification, when players are reserving their event of up to 12 players, should they be factoring in some of those 12 players being NPCs for the private event? Based on the info presented in the original post it would be my guess that that is the case, but wanted to double check as it was not clear. In addition, for purposes of maintaining the 3:1 PC:NPC ratio should players planning one of these private events factor in the staff running it as NPCs or part of the 12 player limit? Assuming the 12 player limit does not include the staff running the event, that would allow for a maximum of 9 PCs with 3 needing to be NPCs. If the Staff are considered NPCs for purposes of the 3:1 Ratio, that number can change slightly though.
Think this is a cool concept and am interested, but wanted to get clarification on a few items. Can DM if that is better.