We're from the Buffalo area. I have driven extensively through Toronto for my job as a truck driver. If you can handle Toronto traffic, Chicago is not much different. We've gone through there a couple times and haven't had any problems, but we did it relatively early on a Sunday. Also, I would cross at Huron, you'll avoid NYS tolls and I believe it'd be shorter.
Along the 90 in South Dakota, there's the Corn Palace in Mitchell that's interesting. There's a Cabela's in the same town to overnight in for free. Before you hit Rushmore, there's Badlands National Park which is awesome. We stayed at Rafter J CG near Rushmore, loved it. People will say to visit Wall Drug between Badlands and Rushmore, we never have, seemed like a tourist trap.