I live in Wisconsin and travel along the west shore of Lake Michigan frequently. You will get a few views of the lake from the interstate but not many. Most of the trip south on the I will include metro areas. I would stick to the state roads.
My preference for a trip suck as this would be to go across the UP of Michigan, visiting the Apostle Islands, Porcupine Mtn St Park and Keweenaw Peninsula, Sault Ste Marie, Mackinac Island & bridge. Take your time going across the UP, there is a lot to see.
Door County Wisconsin is great but you can spend a week there and not see it all.