Bud,
I'd highly recommend the car ferry... a lot of additional lighthousing opportunities if you do.

I assume you'd come across Michigan on I-94, where you have a bunch of alternative routes up to Ludington.

If you take I-94 to Benton Harbor/St Joseph, you can catch the St. Joe's light and then work your way up the coast and see South Haven, Big Red in Holland, Grand Haven, White River, Muskegon, Little Sable, and then the Ludington Pier light near the ferry terminal and just about 2 miles north and a 1 mile walk, Big Sable Point. If you're into whirlwind, you can do that in a day, but it's a very lonnnnnnnnnnnnnng day! I'd recommend allowing yourself 2 days to do the Lake Michigan shore from St Joe's to Ludington.

The ferry ride across is always great in my opinion, and it gives you some views of Manitowoc that you can't get any other way. The other MAJOR PLUS as far as I'm concerned is that it cuts about 8 hrs of driving off getting to Manitowoc if you go around the bottom of the lake and through Chicago. Well worth considering I think.

Let me know if you would like any additional info on the ferry or the Michigan lights here in my "back yard."

Gary