If you plan on being anywhere on the Great Lakes, you need a Coast Guard captain's license and an inspection from the MDNR both. Pretty good cost the first time through. I think there are more details in the history on this site if you search for it, but go to the USCG site (I believe the captains for hire stuff is out of the Cleveland office).
There is a local outfit that teaches the captains certification course. I'll look around in my stuff tomorrow and see if I can find the info. I was going to take it last year but it was too pricey for me at the time. I'm sure there are Captains on LSCN that can help. Try posting in General Discussion or one of the other boards. Good luck.