Ok, let's try this again. North Manitou Island. Take the ferry over Friday morning, then from there the discussion begins.
The issue tends to be a back-up plan if we can't get ferried across. There are a few options here. In the other thread, it was mentioned to move on down to Manistee Natl Forest for the NCT or MRT. Another option is to roll on down to Sleeping Bear Dunes and head into the backcountry there. Third is Nordhouse dunes.
Just a note, average temps for Leland, MI in Sept is 70 high and 49 low. But weather is pretty unpredictable.