I certainly think the committee should be small. In my own experience small committees are much more focussed and effective.
I don't think that (at this stage anyway) members need to have specific roles or job titles, with a few (obvious?) exceptions. There should be a chairman/woman/person to take charge of meetings and generally chivvy and bully everyone along. There should be a secretary, whose main function should be the keeping of records of meetings etc. And it seems to me there should be a treasurer. As Mr & Mrs Hedgehog pointed out, there will surely be expenditure, in the future if not immediately. Individuals may be happy to stand out-of-pocket expenses themselves at the moment, but that shouldn't be a requirement of the job, and in any case expenditure could grow in all sorts of unexpected ways.
My preference would be a total committee of perhaps six or seven, including the above mentioned three (normally called officers of the committee), and three or four ordinary members without specific roles.
If the elected committee should decide to put individual (already elected) members in charge of individual areas then that would of course be entirely up to them, and likewise if they should wish to co-opt non-elected people to take charge of particular areas they could. If co-opted members only attend meetings that they're requested to be at then the thing remains small and manageable, and doesn't become an overgrown talking shop.
Finally, like marinor, my vote would go to <.quote> the people who had the foresight (and bottle) to set GAGB up in the first place<.endquote>.
Do not go gentle into that good night.
Rage, rage against the dying of the light. (Dylan Thomas)