We cannot downplay the significance of size. If you want to better understand at least one aspect of the complexity of the American church this from Mark Chaves' post is worth a look:
Size is among the most important characteristics of any organization, including congregations. It affects everything else. More people means more resources, more staff, and more programming. Bigness also brings more complexity: different kinds of staff, more administration, more attention to coordinating the various parts. Bigness brings bureaucracy, formality, and a loss of the personal touch. Some may worry about churches that get too big for the pastor to know all the members’ names. I once heard a megachurch pastor confess that he didn’t know the names of everyone on his staff.
There is lots one could say about congregational size, but one fact is fundamental: Most congregations in the United States are small, but most people are in large congregations... ~ More from Mark Chaves