Interesting questions. I do not have time to address them. However on your Question 18, Harry Turtledove wrote a book called Guns of the South. It is a sci-fi story about people coming back from the future to supply the South with AK-47s.The result is the South wins the Civil War. From there he has a whole series of books that take off on the premise of the South having won the war and yes, they eventually have to fight again. You might give it a look.
I had that book recommended to me in a previous thread and that might be one of the tomes I get along with Foote’s trilogy.
Actually, Guns of the South is a stand alone book and not part of the Alt. Hist. series.
That series actually starts with a Confederate victory at Antietam in “How Few Remain”, with no Science Fiction thrown in.