[gjbingham]

I'm not sure what the answer is for your specific case regarding the size. Larger makes sense to a point, but the oven will stay hot for a long time and multiple loads of bread and food can be cooked from a single firing.

I think you should do a lot of research to make sure that it will serve your communities needs. The Bread Builders, written by Daniel Wing and Alan Scott is an excellent resource and sounds like the type of ovens that you're looking for.

Canuk Jim will no doubt have an authoratative answer for you soon.