It's great you've given this all some thought-even if the night is horrible (which it probably won't be-I'm sure it'll be fun) it's already brought you a lot of value because you've thought about things, learned some new things, broadened your playing and your perspective. I wouldn't worry about making some kind of gaffe, it sounds like you are pretty considerate in how you are approaching it and the other musicians and you stand to have fun and meet some like minded musicians.