Audio: Ask the DJ to hook up your tascam / zoom to their soundboard OR if they have an SD insert on their audio board, get that as backup, DJ's usually have a mic, ask the officiant if he can give the mic to the couple as they talk; Mic up the groom as well, sometimes the officiant isn't great about passing the mic. 

AUDIO is extremely crucial, PLEASE please PLEASE do not skip on it.