My home port is Duluth,MN and I even get to live here year round. I actually work 5 minutes from the boat.
Here are my thoughts about a long trip into lake superior from Michigan. 4 years ago I brought my Catalina 27 from Traverse City to Duluth, MN up through the Soo Saulte Ste Marie, Mich. It was a great trip in which I will do again someday soon. We pushed and did it in 10 days. That included 2 overnights/days in Houghton, MI for weather window and 2 days in Apostle Islands(which is awesome) Anchorage delight. Not that crowded.
Other posts are true...There is some vast open parts but there are some great ports on both the north side and south side of Lake Superior. The best reference is Bonnie Dahl's Superior Way. It gives depths, amenities, and any other information you need about the area.
Isle Royal is also a popular place where you can observe the predator prey balance between the moose and wolves.
Okay to answer some of your questions.
(1) traverse city to Mackinac Island Maybe I am just a deep water sailor but it freaked me out to have to worry about the channel in the rock.
(2) St mary's River. Be sure to have good charts and start early in the day. I did it at night in the downbound lane. Learned some lessons. When channels come back together it is a light fest
(3) You must have an auto pilot or forget it.
(4) From whitefish bay until keweenau pen. Is a trek. Can also take the canel... Very pretty through there.
(5) The strech from keweeneau to Apostles is a pretty long dark strech if you don't stop in Ontonagon.
If you have any questions please feel free to PM me and I will gladly field any questions you may have..
Get out and explore