As far as avoiding I-80 south of Chicago, we travel from Champaign to west Michigan (Grand Haven) frequently and we get off I-57 at Kankakee (exit 312) and head east and north on IL 17 which eventually turns into IN 2 at the state line. We take IN 2 all the way thru Valparaiso to US 421 at Westville and then north to I-94 (there is an interchange to I-80 off 421 also). We also "cut the corner" on IL 17 at Momence by taking IL 14 to IL 17 and avoiding going up thru Grant Park.
Overall, this route saves about 10 miles vs going I-57 to I-80. It's definitely not faster (unless you get involved in a traffic jam on I-80) but does avoid the worst of the Chicago traffic. We drive it with our car and motorhome but our kids say that it's too much bother and just prefer the I-57 to I-80 route. (The I-57 to I-80 route does include a $1.10 toll on I-80 as well so we avoid that by taking the IL 17/IN 2 route.)