I'll pass on what I have learned from attending many non-MV events.
The essential measure of success is that people are having fun.
There will always be people who thought it should have been different. You shouldn't have charged anything, you charged way too much, you didn't charge enough. You should have hired a better live band, it should have been country, not jazz. There was not enough food and beer, the food wasn't good enough. It was too far, too expensive, the tee shirts were the wrong color, the stickers were too small. Not enough or too much of something. Too many rules and too strict or not enough
rules.
The larger the group, the more of this ^^ you will hear. It's group dynamics and it's a real pain.
The more complicated and full featured an event is, the sooner the organizers will burn out and the less fun they will have. The most common refrain from organizers is "next year you do it" or "never again". The chances are pretty good that the organizers will end up subsidizing the cost of the event to some degree.
Still want to do it?
What works:
Let people know that they bring every thing they need except for the portable restrooms, and that there will be a nominal fee to cover the cost of those. Order twice as many as you think you will need.
If people are entirely responsible for bringing their own fun, food, and drink, it creates a much more relaxed atmosphere where those deadly expectations we have of others are not a problem.
When you attend:
Bring lots extra of that signature favorite dish you are famous for to share with everyone. Bring with you an attitude that you are responsible for your own good time, and think of what you can do to add to others enjoyment.
Leave behind:
Any expectation that others will do what you want them to do.
As far as a turnout goes, if two people show up, count it a success!