Here's a comparison of Indiegogo, Kickstarter, and GoFundMe.
I think most people are gonna be fine with you starting it, especially if you post receipts. I'm not 100% sure, but it might be better to wait till we're closer to the day of the potluck- we'd have more subscribers. The other option would be to just leave it up for a long time. Still, we'd have to wait a reasonably long time from now before we can actually start purchasing things for it, since it could potentially get really big quite suddenly. Hard to say with the internet.