The biggest challenge would be encouraging growth with people outside of your base.

You become a $50m company, and the young manager you hired is turning out to be better than your sister/brother/wife/husband... are you ready to replace one of those people with an outside person?

As an outside individual I tend to be wary of working for a family run business because the chances are that I will never be able to replace the owner's wife/brother/sister/husband, instead my maximum growth will be the tier below the family.