Well, a definite congrats.
I have to agree with BBQ Bubba though. A big festival may not be the smartest place to start. I understand "BiG" is relative. County fairs in MN and TX are bigger than state fairs in most other states.
Talk to those that run the festival, and get some contact info for vendors that have been there previously. Buy them a cup of coffee and get some serious answers that will save your ass. Expected head count; how much do they expect to sell; is their menu 10 items or just 5(compare with yours); how much cash to have for change; equipment tips (maybe they are full time and would rent some to ya); and so many more questions.
To hold pulled pork at temp without drying, keep them wrapped in foil inside a thermo box (hot box). As soon as you pull pork or slice brisket it starts to dry. Keep it whole and wrapped as long as possible.
Checklists, prep, and planning will make it as simple as you can get it. That may not make be very simple, just as simple as its gonna get.
2 - WSM 18.5, 1 - WSM 22.5, and 1 - ECB Smoke n Pit.