How Big Should An Estate Agent's Board Be?

It can be any size, depending on the functions it needs to perform and the number of people required to do those functions. If a board comprising of two members is enough to fulfil all the necessary obligations and tasks, then that is all the members you are going to need. If the functions in mind are more complicated and require a larger number of people to execute them, then that's the number of people you need.

A board's working does not depend on how many members it has, but how well each member works and completes his tasks and duties. The only specification you need to keep in mind is exactly how many members will it take to do the job, two or ten? If you have the answer to that, then you have the answer to your question. You do not need any more or any less than the number required.