The 24 will give you the equivalent of a 36 ( I think !) which is fine for candid shots of the ceremony etc & you will get some flexibility with its reach as well, I just think that you may be struggling for group shots & other wide stuff if you are working in tight spaces. Do you know which shots the couple want, where they want them & can you take your gear for a trial run for angles, obstructions & best locations? That will give you a better idea of what you need for the day. Also you would get an idea of lighting in the venues, eg, will the f4 be fast enough in an old church on an overcast day?