Originally Posted by IPassGas

-You will want fenders/mudflaps. The C&O path is very muddy especially in June. After Cumberland, the GAP surface is excellent in comparison. But even after the C&O, it often rains that time of year in Pennsylvania/Wisconsin/Michigan. A weather radar app on phone is handy. Wisconsin has taverns everywhere to hold up in during storms.

-Amtrak is very slowly improving but can be a pain with bicycles. The train service in US is very poor in comparison to Europe, the train (only one 1/day?) often runs much later than stated. If there is no "roll-on" service between Pittsburgh/Milwaukee, you will need to box bikes at Pittsburgh/Milwaukee. As an option, you may consider renting a small truck one-way. UHaul is everywhere and the price for 2 people is comparable to train.

-Appears to be good bike way north from Milwaukee (not biked it). We have biked from Sheboygan (Wisconsin) to points north. As a suggestion, you could bike (we have) along the Lake Michigan shoreline the entire route...Sheboygan, around Door county peninsula, Green Bay, north to Escanaba (Michigan), east to St. Ignace, south to Muskegan and take ferry back to Milwaukee. Roughly 3 weeks. Try to stay on back roads with the word "lake" and/or "shore". The Delorme paper atlases are great, but not required if have smartphone.