Couzens was also mayor of Detroit. Couzens sister was a teacher and invested $100 in Ford at the inception and ended up getting $262 thou out of that investment.
The Dodge brothers were also investors and made a fortune in addition to supplying many parts for Model Ts. Their earnings helped them finance their own competing car company.
FMC was Ford's third attempt at a car company. The third time is a charm, I guess, as this company was successful almost instantly. There were many who were instrumental in the success of Ford Motor Company, Couzens probably chief among them. Harold Wills was another contributor to the engineering of the Model T. Henry was far from alone in the success of Ford, although he had the vision.
Ford wanted to continue to invest in the company and his shareholders wanted dividends. It ended up going to court and Ford lost. He eventually bought everyone else out through a variety of means.
Here are the original investors. Some didn't make out so well
https://www.thehenryford.org/exhibit.../investors.asp
Charles Sorensen was one of the few around in the early days who stayed on. A fascinating story of a business. There are some very good books about the history of Ford, not all of it pretty.