> Anyone have any stories or examples of ... large co-founder groups?

From my personal experience, it is very common to see startups founded with many co-founders. I've seen it a lot in college groups, where one individual is very motivated to bring in their friends with specialized skills.

Unfortunately, the high speed stage of startups where anything goes, and any one founder's ideas can define the product does not last for long. This often leads to a smaller, more refined group of founders.