What should I tell my audio vendor before an event?

The most useful information for your audio team upfront: venue name and room dimensions (or a floor plan), expected audience size, whether the event is speech-only or includes music/entertainment, the full program schedule (including transitions and segment types), the number of presenters and their microphone preferences, whether there's a livestream or recording component, and any known venue restrictions (noise ordinances, rigging limitations, union labor requirements).

Also share the power situation (available circuits, generator needs) and whether other vendors are sharing the same power supply. The more your audio team knows early, the more accurately they can spec the right gear and crew. A tentative schedule or draft floor plan is better than waiting until everything is final.