Perhaps a slightly odd question... I’m preparing the vocal score for a two act opera and was wondering whether it is standard for numbering to continue throughout the whole opera or to start numbering at 1 again for each act?
Yes, the numbering restarts at the beginning of each act. This is standard across all subgenres of opera.
But intra-act numbering conventions vary depending on the style. If it's a number opera, the measure numbering restarts at the beginning of each number. But if we're looking at a continuous single act (like those in Wagner, for example), then the numbering will continue for the entire act.