i'm going to bring my girl 18mths to europe in end oct. we're going to italy and spain. i think weather wise for you in december have to bring some winter clothing for your baby.safety-wise i'm bringing my baby carrier which my girl can still fit in so she can be strapped in at crowded places, and do be very careful of your valuables.
i believe you can pump in plane but probably have to pump in the toilet which can be tough. i normall latch my girl direct.
hope this helps and enjoy your trip!