We did the ship's tours in St petersburg as we had a late booking and didn't have time to get visas or book thru an alternative source.
We had some very good weather but also some rain. Suggest that you take a kagool, that can be folded down and carried in a bag. that way if it rains you can still get about.
My currency was ordered from the bank before travelllng, that way you avoid the queues that are always at the pursers desk.
Hope you have a good tme.