Have you contacted other co-ops around the country to see how they are set up? I can think of three in Chicago, different sizes and in different parts of town, with somewhat different focus in each one. I've been to two of them; they seem to be thriving, at least from the amount of activity I see at them. Both of those have a retail operation, selling fixed-up bikes at decent prices. The larger is only open two half-days a week---when I was in there Saturday at 1 they'd already sold 36 of the 40 bikes they had prepared for the day!