There are quite a few places that can accommodate smaller weddings, and some are really QUITE lovely!!! I just got married in South Haven last summer and everyone is really helpful. Most of my centerpieces were from the stores all along Phoenix Street.
The Visitors Bureau put together a list of places that hold wedding receptions (and most have numbers of guests they can hold). They can email it to you if you give them a call. Their number is 800-764-2836.
We had our ceremony on the beach and personally used mybarefootwedding.com (Bryan was helpful and responsive). Our reception was at the Beach Haven Event Center (which holds a larger group, up to 300), but there's tons of places you can choose from if you work early enough and know how many guests your party will have.
You can even get blueberries from DeGrandchamps Farms and hard cider from McIntosh Cellars (it's delicious and local). If you have any other questions, or if I can help with more vendors or details, let me know! My email is email@example.com.