a) Race and Reunion: The Civil War in American Memory, the book in question reviewed by Eric Foner actually sounds to be quite interesting. It goes over the post-civil war debates in america, the peoples’ attitudes towards the result. It also focuses on the accounts of black press of the time.
b) Yes. However his summary of the book seems a bit dry, that is understandable as when you cut everything besides the main idea out, you lose content. Although I am pretty sure nobody here would want to read a 20 page summary.
c) He refers to it as a “cottage industry”. Now a cottage industry usually exists in places like secluded villages which prove self-sufficient every person makes a different thing and they trade between each other. My interpretation of that is that people and various groups consisting of historians or not, come up with their own views and ideas on the subject and then they share them and debate them (something like a smith trading a hammer for a pair of boots).