I've only ever been once before myself, Simon ... for 2/3 days during August, 1997 ... less than a fortnight before Diana, Princess of Wales' fatal car accident, in fact. I [think] I might even have SEEN the spot where it subsequently happened ... a "creepy" thought, really!
We shall certainly be taking full advantage of the Metro for getting around and, hopefully, visit Montmatre, as you mention.