Mark,
Manitou is part of the Sleeping Bear area, but the island doesn't allow any vehicles. You (being out of state) would need a pass to enter the Sleeping Bear park specifically. But the islands transit system doesn't require a car sticker to park at their parking lot. Just pay for your ferry ride and backwoods pass.

Once on the island, camping is allowed anywhere 300 feet from the waters edge. We set up camp, then lollygagged at the shoreline. Some folks fell asleep in the sun for waaaaay too long.

As Dave mentioned, sometimes the crowd is giddy. But for all the panic at the ranger station/dock, once everybody spreads out, you rarely see others. There are some really popular sites, and those do need a foot race to secure. But for a hammocker, there is always two trees.

The ferry only runs in good weather. The wind and waves can get sketchy, safety first is the rule. So be prepared for an extended stay, if the weather does not cooperate. The ferry may drop you off, then not be able to pick you up at the designated time/day. So flexibility is key.