Cameron, that's an excellent question, but I'm not sure there is a guide like that. Hopefully, I'm wrong, and someone will have a specific recommendation. But because laws and regulations vary so much by state, county, and
city, such a resource would either be too vague to be useful or so detailed that it would be too expensive. The book you mention is a good example. Then too, laws and codes change all the time.
As you surmised, "build to code" refers to whatever building codes your building location is under. They apply not only to new structures, but also repairs. We had two properties we were interested in buying fail inspections because the repairs weren't done to code. The codes can usually be found on the county website, but of course, that means you have to have a specific county in mind. Perhaps as preliminary research, you could pick a county in each of the four states you're interested in and check their county websites to make a comparison. Might give you an idea that can help narrow your search.
Besides building codes, you will also want to research livestock laws if you plan to have livestock, and fencing laws. Every place has it's own definition of a "legal
fence," which is important to know in case your neighbor's herd of
cattle ever bust through the
fence and help themselves to your garden.
P.S., I added your post to the "Midwest USA" forum, so perhaps it will catch the eye of folks who live in the states you mention. They might be able to give you more specific information.