The internet in many ways eliminated the need for such cooperatives. Everyone who can afford to place a monthly add in the back of B&W can afford a pretty nice web prescence. And anyone who has done searches of sites knows there are thousands of photography sites.
Now it seems that things have come full circle. Even the best photography sites get lost in the heap. I have read about very few photographers who sell prints over the internet, and the few that do so I don't think are living in luxury unless they have income from commercial and gallery sales.
Now in order to stand out from the crowd you have to have presence like ads B&W and be actively soliciting galleries and individuals. I think a continuous 1 or 2 page advertisement shows you are serious. What shows you are more serious is if you can post a gallery showing somewhere in each issue.
That means a person(s) needs to be actively sending to or visitng galleries with a portfolio of the artists. They see the ad every month, they are more likely to take you seriously, maybe not accept the work, but have more consideration. I don't think the ad or a website will sell prints on its own. There has to be that personal contact and aggresive effort to get work out to people.
I agree that one person needs to make decsions. Feedback and suggestions should be taken, but there needs to be a "director" to be final arbitor.
Finally, you will need to be pretty merciless when it comes to deciding who gets to be involved and what prints are selected. I would suggest that perhaps you solicit (pay for their time) a gallery owner/director or museum curator who could help you decide on prints or give input. They would have a more objective POV and have a better understanding of the marketplace.
Personally, I would rather be rejected because my work was crtically evaluated and judged not to meet the co-op standards, then be accepted because my money helps defray the costs. Besides, that just gives me incentive to improve my art and craft.
It seems it would be much more successful to have a small group of dedicated artists, rather than a large group that might have some individuals who would demand results for the money they put in.
Just some extra thoughts,