Some quick comments for our visit to Copenhagen, Stockholm, Tallinn, St. Petersburg, Helsinki, Bergen and Olso:
with so many countries, my worry about currency was a waste of time. Credit cards are used virtually everywhere. Might want some currency for transport or a postcard or two but lots of money not needed. That said, found flea markets and weekly markets-cash only.
Always ask for senior discounts, age varied (one you had to be over 67) but from buses to trains to museums, it was available.
Nice location on ship but on our trip, really got no sun.