The Baltic is a wonderful itinerary and you are sure to enjoy yourself immensely. You can do virtually all of the ports on your own with the exception of St. Petersburg. You can find detailed information about each port at www.PortReviews.com
. The issue with Russia is the availability and cost of a Russian visa. If you do not obtain one, then you will have to use the ship's group visa (only available on ship sponsored shore excursions) The ship will generally have private cars/vans available for hire with an English speaking guide if you want to strike out on your own. This is an excellent option if you want to do something other than what is offered as a shore excursion.
Be sure to share your experiences when you return by writing a review.
Have a great cruise!