Solid, welcome. Neither my personal experience nor my study of audio technology has indicated that there are significant problems in the areas that you mention. When oxidation(which isn't green)occurs from external causes it should be cleaned or trimmed off at the point making contact with the terminals. The electromagnetic wave carrying the energy and signals which travels along the outside of the wire isn't affected by the stranding or other variations in the interior of the wire. Belden or other makes of lampcord of an appropriate gauge for the distance of the run are fine. Brass is an entirely appropriate material for the straps connecting the speaker terminals, and designers wouldn't sabotage their own creation with something that harmed the performance.
