Duluth Rally/Reunion

Coming from St. Louis, MO and touring Minnesota for the first time before meeting at the Duluth Rally we want to see a lot and stay a several parks. My question is: that time of year in MN are reservations generally necessary? We don't really care for private parks and mainly prefer state, federal and COE (expecially with the geezer pass). Typically when we travel we only make reservations on the weekends and that's only during the summer months. Our logic is we never really know where we'll end up for the night.
One of our goals, being from St. Louis, is to see the start of the Mississippi River. And other from that we're open to adventure. Two asthmatics with bad knees who like to walk,  history, the unique, sights/scenery and quaint/local eateries.
Any and all replies welcome.
Thanks and we need your help.

We've toured Minnesota several times but always in the Fall.  For the summer I'd be sure to have reservations for the weekends no matter where you stay and during the week I'd have them at the big name parks like Itasca (where the river starts) or Bemidji plus any park along the Lake Superior shore.  The nice part of the Lake Superior parks is you can make one of them in the middle of the route a home base and check out the others from there.  A few don't miss 'em places are the Soudan Underground Mine, https://www.dnr.state.mn.us/state_parks/lake_vermilion_soudan/tours.html The Hill Annex Mine https://www.dnr.state.mn.us/state_parks/park.html?id=spk00176#homepage and the International Wolf Center http://www.wolf.org/ The only Minnesota State Park I've ever been disappointed by is Schoolcraft, it's quite outdated, few if any level spots, narrow campground roads, and very wet.  Beautiful spot though, worth a visit just to see how quickly the Mississippi gets big but I wouldn't stay there.

Hope this helps!
Gary