Not sure about in the US but here's my experience in the UK having just done my first year at Craft Fairs.
I think at the outset decide why you're doing the Fair. For me it was a way of marketing myself as a photographer in a new region we've just moved to.
On size - the decision to buy a print at a larger size is one that I think buyers make over time - would you want to spend that much money on a print that may not fit in the place you envisaged it? My idea was to have small prints, mainly 6" x 6" square because of cost, and offer larger prints by pointing people to a website to help them make a choice at a later date - business cards/ websites etc are important and ask for the email address of buyers or interested people so you can follow up.
Buyers, on the whole, don't appreciate the benefits of a SG print over digital - they don't care in most cases. The subject is more important. A print I sold, for instance, was of Paris, France, and the couple who bought them had been there and were collecting images of Paris as reminders.
On my last fair I displayed a 1910 banquet camera complete with brass lens and this opened the door to give people something to talk about. They then asked if the images were made using that camera and the conversation and selling goes from there. I was reluctant to do this but my wife persuaded me and it worked. There was something unique about it.
I sold only RC prints but if someone was sufficiently interested would offer archival fibre based.....had no takers at present!
I decided to display, on small wooden easels, my mounted prints - only around fifteen at a time and had a smart box with another fifteen in. The digi-boys at the fairs I did had thousands of images in many boxes. I wanted my buyers to be able to see and make a choice rather than be overwhelmed - it worked reasonably well. And the one thing about displaying this way was that people actually stopped and looked and took time - which was great to have people interested in your prints. The hard part is converting that to sales.
I'm still learning!