A few thoughts:
I agree that you would need to run at least a one page layout to get any kind of attention. My own experience with B&W is that I take the work presented at the front of the magazine (usually the full page or double page ads) as the most serious collectible work. I think you really need to be among pages that contain advertising for galleries and current exhibits to achieve a certain cache of "being there" as opposed to the 1/4 page adds in the back.
Also it seems to be my impression that artists who advertise a lot seem to get spotlight articles. I have no opinion about this practice, but maybe a full page or eventual double page add would give one or two coop members a leg up in getting a spotlight feature.
Finally, I think you need to determine the number of members and cost per member and present that. Then decide on a procedure for accepting members to the coop. And be prepared for some one getting mad at you if there work is not accepted. I might submit some work for consideration and if it is rejected I would just try another time. Some people might take it kind of personal about it.
If it happens I will look forward to seeing it in the future.