Big job, and the hard work really comes after with the printing and order filling etc.

Are you shooting with tethered DMF (Medium Formats), DSLR's or chip n' carry's(the commercial store cams with the photo card) or film . . . ?

If there are very many children involved 20 seconds is not probably going to be very close to average. I'd allow at least 2 to 3 minutes per, on average, for everything. Stools get knocked over, people are different heights and you have adjust lighting or find a box to stand on, people stop and talk. Give yourself a little cushion.

I'll think on this and try to give you some more ideas in detail later, particularly with 3 shooters and keeping everything straight regardless of of format.

- CDP