Yes, plan above the base count for your headcount, because 8 hours, food vendors and a mostly female crowd each push you up a row on the operator's chart.
When I booked units for our church harvest fair, the operator asked four things before quoting: headcount, hours, whether food or drinks were served, and the rough split of men and women. The units per person charts most of them work from follow the PSAI guidance, and every one of those factors moves the number. Give them all four up front so you are not guessing off a generic table.
For accessibility, the 2010 ADA standards say that when portable units are grouped together, at least 5 percent of each cluster has to be accessible, and never fewer than one. Put the ADA unit on the flattest, firmest patch of grass near a path, with the door facing the crowd.
On unit type, standard units are fine for a dry daytime fair. What made the biggest difference for us was separate handwash stations near the food row instead of relying on sanitizer inside each unit. Your health department may require that anyway with food vendors.
Last thing: ask for a midday check if the fair runs all 8 hours. Paper and sanitizer ran out on us around hour five.
