I would say let the organizers decide what they want it to be...a community that can struggle to make pretty music but enjoys themselves, or a group of people who really want the music to be primary..these are two different groups of people and generally are going to be somewhat oppositional although generally polite. The latter group will just drift away if former predominates generally..and it is fine if they do..would be nice to have at least two types of groups and they can go to which one they prefer.

I recommend seveural things:
1. Decide on the book issue right away. I think the best compromise is to use them for yourselves but dont have the whole group using b ooks.
2. A Decide right now about electronic devices..people will bring ipods etc. for words and decide if that bugs you or not.
3. No flourescent lights at least the old strip ones..people look ugly and it makes the music less inspiring. Some darkness is good..poeple can bring their own flashlights if they need to illumimne the book they might have brought.
4. Limit the diameter of the circle..this is a huge insight I had recently...sound of the music is inversely proportional I think to the diameter of the circle. Do not let the size of the room affect the size of the circle...have a good diameter..it will vary with the group, the room acoustics etc..but people should be able to see each other and know they are in a group activity..form additional circles in back of main circle.
5. Just saw a smart guy at singtime in portland have laminated cards that people pickied up when they wanted to sing..avoids the whole thing of zigzagging back and forth as new people come in, getting people in the back etc.
6. have some good leaders and some good strong sopranos who can lead the group. Good music is made by some combination of good followers and good leaders and when people defer to others who are better at leading...some poeple hate this so then they should be in the community group...some people are fine with leading and following roles, which will change with various factors...one day you are the windshield and the next the bug etc.