We went on this tour several years ago and loved it. We arrived in Tallin a few days early. It is a wonderful and charming city with a wealth of history.
I would certainly take advantage while being in russia and travel. We took the train from st petes to moscow. Please check out some train forums on the internet for advice on how to travel on these trains. Unless things have changed at st petes train station please be prepared for no english to be spoken. You can buy your tickets at the station, but when we were there there were long lines and many people butting into line ahead of us. It would be helpful if you had the tour guide write a note with your destination (moscow) or whereever you intend to go, because as I said there is no english. Get there early and prepare to wait for the train. The train announcements are in russian which can make it difficult.We were lucky as there was a conference going on so there were lots of young men who spoken perfect english who were very happy to help us.
We bought our tickets ahead of time and picked them up at a travel agency (cant remember the name) who also arranged a our guide for our 2 day moscow visit. Moscow is so worth while. Red Square, Kremlin etc. The cemetery of the 2nd honour, university. Try to get tickets to the bolshi ballet (I know they can be expensive) but same day are cheaper. It is so beautiful inside, we were overwhelmed.
There was not alot of english spoken in russia, except for the younger generation. Try to run the subway. It is absolutely breathtaking with the paintings etc downstairs where you catch the train. Be prepared for people to stare at you somehow they just knew we were foreigners, but a smile goes a long way.
We then went on a tour to the golden ring and lake baikal(?). We wanted to take in as much as we could, as we didnt
think we would be back.