I have no idea if you are the type of travelers to stay in hostels or not, but there is an HI hostel in DC. I stayed there for three nights after I rode the GAP and C&O before getting on the train to come home. It was my first trip to DC so I wanted to stay for a few days and see the sights. Hostel is much more affordable than a hotel in DC. They had a small shed out back in a secured yard for people to lock up their bikes. But, some people might have a stronger preference for hotel. That hostel had a prohibition on alcohol on the premises, I only mention it because some HI hostels don't.
You might want to stay in DC for a day or two to try to change your internal time zones, if you stay there for a few days the Smithsonian is worth seeing. Several buildings, pick the topic that interests you the most. I am a geological engineer by training, so I spent two days in the natural history museum.
I camped in Cumberland across the street from the YMCA, but that was eight years ago, I have no idea if that is still an option, when I was there the fee was cheap and they had showers. I do not remember much else regarding where I stayed when I rode that trail. Cumberland is where the GAP and the C&O meet. It is easy to think of them as one bike trail, but they are two separate trails that meet at one point.
You would change trains at Chicago. If you were in Chicago for most of a day, a walk over to the Field Museum could be a good way to kill some time.
Most camping stores would sell butane canisters such as you would want for most MSR or Primus type stoves. If you are using an alcohol burner, maybe buying alcohol fuel at automotive fuel stations is the simplest thing to do. Often you can buy small bottles of alcohol as a fuel deicer, I think the Heet brand in a yellow bottle is Methanol.
July 4th is a USA holiday. This year July 4 is on a weekend, most campgrounds would be full and you can expect it to be a three day weekend. Thus, that weekend is one you might want to plan ahead for. In USA, generally you rent an entire campsite at campgrounds.
Wisconsin, in general terms you should assume that you will be at elevations that range from 200m to 500m in elevation. There are some hills, but none should be too tall.
You will want to have mosquito repellent. Some places will be buggy, some not so much.
I do not think you will find a bike shop in all of Wisconsin that has any Rohloff supplies. I think I previously suggested you bring a spare internal gear cable, just in case.
I do not know Milwaukee well enough to know what parts of town you should avoid, but it sounds like you are getting advice from someone that posted above.
I live 90 miles (~~140 km) west of Milwaukee, but have not been there in several years. I have actually done very little bike touring within Wisconsin, most of my touring has been elsewhere. So, I am a poor person to advise on touring opportunities.
Send an e-mail to Wisconsin DNR and ask them to mail you any information that someone that wants to camp at their parks and maybe ride on some of their bike trails would find useful.
https://dnr.wi.gov/topic/parks/
I have no idea if the DOT has any useful information or maps, but you should send them an e-mail and ask them to mail you what they have for bicycle touring in Wisconsin.
https://wisconsindot.gov/Pages/trave...aps/state.aspx
If you get up to the UP (upper penninsula of Michigan) that is Michigan and not Wisconsin, contacting Michigan state park system ahead of time to find out where their parks are may be useful.
Generally the bike shops in Wisconsin would have 26 inch wheel tubes and tires, but the tires are likely to be mountain bike tires. Good 26 inch tires for pavement riding are less likely to be found in most bike shops.
It should be pretty easy to buy just about anything you need to eat at most grocery stores. Almost all grocery stores will take credit cards, but you might want to carry some cash too. Some of the really small stores you might fihd in small towns may prefer cash to avoid the fees from credit card companies.
When I have gone touring outside of USA, I never bothered to get a sim card, instead I always used my phone was a wifi device. Sim card, I have no good suggestions - but you will find many of the cell companies here use a system that does not involve using a sim card, thus some phone companies would not be an option for you. I think that generally sim card cell phone companies include AT&T and T Mobil. You might want to make sure your phones work on the right frequencies here. North America might be different than you are used to.
https://www.worldtimezone.com/gsm.html
If you are wondering about weather conditions here, I live in Madison, this website has good data on average temperatures, average precipitation, etc. You can type in any community that has an airport and get local information on that area.
https://weatherspark.com/y/12796/Ave...tes-Year-Round
For daily forecasts, the national weather service has pretty good forecasts, I usually just use that instead of some of the other apps out there. Type in a city for forecast, Wisconsin abreviation is WI. Thus, if you wanted forecast at Milwaukee, type in Milwaukee, WI in the upper left corner.
https://www.weather.gov/
If for example you were on the Milwaukee forecast page, down on that page you would find a link for hourly forecast page, click on that and you get this.
https://forecast.weather.gov/MapClic...Type=graphical
I like that hourly forecast page because it gives very accurate wind direction and speed information (miles per hour). And temp of course is F, not C.
If I think of any more info, I will let you know.