28-75mm f2.8 should be fine...good for general portraits but may not be wide enough for groups shots. Fast prime lens in the range of 35mm to 135mm would be excellent in this environment...to isolate subjects from crowded surroundings.wow it sound like many people to go.... last time i dint got flash so only can get head shot... (cox only got 1xF2.8-90mm lens) ... this time i prepare the 28-75mm .... hope the result come out wil be improve