To answer your questions, I tend to err on the side of citing everything, though I'm not certain what the consensus view at FA evaluations is.  As for sources, I think four books specifically about the subject in question should be sufficient.  Quality of sources has to be considered, and while I don't think four newspaper articles would be sufficient, your sources all appear to be serious scholarly works.  I can't guarantee that this is how the featured article types will view it, of course, but that's my view.  Finally, I think