Well...it's over....didn't go broke by any means and got a lesson or two, so it's all good!
Attendance was about as advertised and we stayed busy. Had a line from 10:30 to 3:00 but never too long. I did run out of some items, but mostly later in the day. Cooked too many brats and I'm not going to admit how many pork butts I had left over

Or buns. Gave a couple of butts and some buns to a local mission/homeless shelter and know what to do with the rest, so that's OK. The event organizer was well pleased and wants to work with me again, plus the folks that own the building want me to work some other events they have upcoming...so that end of it worked well.
Lessons:
Bring more hot dogs than you think you have any use for...they will sell. Same for sodas.
Forget burgers...more trouble than they are worth IMHO.
What is it with coffee drinkers? Lots of these guys bought a cup in the morning and were still coming back for refills at closing time

At least I had plenty.
Know your prospective clientele. I had shared my menu with the event organizer. One of the items was barbequed bologna. She was like...barbequed what? Told me that a lot of the attendee's were "Yankees" and were unlikely to order that. She was right...I even put samples on the counter & some wouldn't even try it...never mind buy it. There were enough good ole boys in attendance that I ended up having one slice left over. I will almost always sell out of that, as many around here seem to have an emotional attachment to BBQ'd or fried bologna. "I want some of that...my Mama used to fix that for me....I was growed up on that".

Works for me!
At any rate...made enough to be willing to do it again...paid my kids and a couple of friends too much for working for me, and had a good time. Wife hasn't taken her cut yet...she seems to think pretty highly of her services, so not sure where I will end up on it! Thanks to everyone here for your comments & wisdom!