I like your northern route. I would dip slightly south and take Highway 20 across Nebraska.
(good 10ft shoulder the whole way across,
here's some video, skip to timestamp 13:30 for good view of the riding conditions, camera mounted on Bob Trailer)
Almost all the small towns have free camping in the city parks (on Highway 20), most of which have public swimming pools with showers. When I went across I did not have a planned route... I just kinda made it up as I went along. I used google to find camping by typing in the word "campgrounds" on google maps and scaled the map to about 200 miles. Its amazing how many campgrounds show up. I also used a website called
FreeCampSites.net to find camping.
On the southern tier I had no problems stealth camping, but in the heartland, most of the land is plowed with crops. Once you get to Wyoming, (and the entire west) stealth camping is feasible again. And remember, you can (with few exceptions) camp in any National Forest doing what is called "Dispersed Camping" for free.
Carry more water than you think you will need.