For an overview of South Haven, go to www.tripadvisor.com
, sort of the 'Redszone' of travel boards. Lots of good info there, usually posted by people that have recently traveled there or locals and includes rankings of hotels, restaurants, etc. plus 'things to do'.
I took a look at the site and they have a good discussion of 'must dos' right now at the bottom of the forum page. It may have sliped to the second page, in case you don't see it.
Here's the link (hopefully) http://www.tripadvisor.com/ShowForum..._Michigan.html
Click on 'South Haven' in the upper left green box for other options.