Streetrod! Yay! Party planning!
Goat people (oh I guess that sounds like a really wierd tribe or something, sorry!) BUT people who raise goats are used to dealing with minority gatherings with a precarious (goat-like) attendance. So, Here's the scoop from my goaty perspective:
Feel out your Audience as you have been doing.
Pick a venue that is easy to reach, and does not conflict with weather and/or holiday plans. Michigan in the Winter is out. Texas in the summer is out. Montana is pretty hard to get to, Detroit is not. But then people aren't scrambling to get to Detroit. . .
I think a main question would be. . .what would STOP people from coming? For me, Children-based holidays are out. So are Fathers Day and Mothers Day.
Here, I do an annual endangered Goat Party (bit more specific than that but there we go) every third weekend in October. I think, if you feel that you have attendees that WILL attend, Pick a day that is reputably sunny in your party region, and start there.
You gotta have fun with it. You CANNOT lose your shirt on it (so make it a potluck! Or charge a small admission!). I LIKE the idea of charging vendors, but start small, maybe the first time is free? Until you truly guage response.
Personally, I would try to come, but it all depends on when and where and health etc (I'm a cancer girl).
From here on in, "if you build it they will come."
Feel everyone out a little, then Set a date (in 2018). Set a place. THEN see who's coming.
My annual goat parties are at my small house. We have seperate guest quarters, and available tent, and nearby B&B places. I offer BBQ chicken and salad and bread and MAYBE another dish but the rest is potluck. I get goat friends coming in from VA, WV, MD, NC, MN, and then also from SC, NY, OH, and PA. And they come for the company. They KNOW that I'll be doing BBQ chicken and salad AGAIN. They're all here for the OTHER PEOPLE who come. And the other people are just other goat breeders with whom they can relate. So. . .you can do the same.
Throw out a few times, see who grabs what, choose a day that's guaranteed to be sunny, and GO FOR IT!