The fact that barn dances are unusual can be enough to attract people. That's a good reason for adding it to your list of fundraising events (probably not if you're in a city though!).
You should have a temporary bar so that you are making money from the event and youll need to consider other items such as heating, power and lighting. If you have a bar, make sure you get a temporary license. You'll need to contact your local authorities to get the details of how you can obtain one in your area.