Lol, you most definitely are overthinking it. For your first time just bring some originals and some prints. If there's specific prints or originals you think would shine with a specific frame, bring some. Postcards are always a quick sell, especially if it's an original piece. I sometimes just buy the watercolor postcard paper from the art store and whiz through a bunch of basic stuff I know people will like and buy. Whatever you do, just relax and have fun :) People buy your work because of you more so than the art itself...at least when it's face to face. At least in my experience. Good luck!