Alrighty, away we go I did a similar trip a year ago, here are my thoughts....
You MUST stop at 18th Street Brewery in Gary, IN. Amazing beer and awesome place.
Backroad Brewery in Laporte, IN would be another great stop en route to Grand Rapids, looks sketchy as hell, but they were amazingly nice to us when I was there (twice now)
Schmohz Brewery in Grand Rapids treated me very well -- it's like a dive bar with really good beer.
Don't rely on locals telling you how long it takes to get from one place to another. Use google maps, I don't know what it is about people in Michigan but they seem to not include time spent driving through a city as time driving.
You could easily spend a day in each town --- Holland/Lake Michigan, Kalamazoo and Grand Rapids. If I had it to do over, that's what I'd do on my next trip.
www.brewerymap.com was a great resource.
Buy tickets and go on the New Holland tour, it was pretty awesome, not as drunk as other tours, but gave a nice overview of a mid-sized brewery and distillery.
Boatyard Brewery was about a mile from Bells and also had really good beer, and was a totally chill atmosphere.
Bells was chaotic, and annoying and overcrowded when I was there. They had a "Beer Hall" atmosphere, no waiting list, no waitstaff, just large groups of people standing, and annoying anyone sitting down "Are you leaving soon?"
Saugatuck brewery had the most unique and best beer on the trip: Neopolitan Stout. It blew me away.