This is interesting. If you can get it up and going, I may attend.
Sorry I really cannot be of any assistance to you with any organizing the event, but you really should be in contact with multiple large locations to see if they would be willing to accommodate the group, and not rely on one location. Also try and get a feel of how many attendees will be going, usually vendors tend to be particular with the amount of people as they want to be able to sell items.
The more the merrier.
GL. If you need any advice I would be more than glad to assist on that end. I used to organize groups for meets for a driving club within the tri-state area, so you can understand how much work is usually involved in getting something like that together.