Fascinating discussion. Zuse told me that he was taught binary arithmetic in grade school, but he only learned of Leibniz's essay on binary (ca. 1680) after Zuse began work on computers. Babbage was an admirer of Leibniz's work but did not consider binary for his engines.  The Z1, which had a binary calculating unit, did not work well, and therefore Zuse adopted electromagnetic relays (a technology not available to Babbage) for his later machines, which did work. Attempts to reconstruct the Z1 for the Deutsches Technikmuseum using late 20th-Century machine tools also failed --  please correct me if I am mistaken. But note that Zuse built a successful mecahnical binary memory​ unit for the Z4, which not only worked well but which was in steady service at the ETH in Switzerland for years. The joke was that the clicking of the Z4 relays was the loudest noise in Zurich on any given evening. The Z4 is now at the Deutsches Museum in Munich.

Paul Ceruzzi