We just returned from the Viking Moscow to St. Petersburg cruise. It was magnificent!
If you have questions or concerns, I'd be happy to help.
Viking booked our flights. We were booked on Lufthansa at incredibly convenient times with perfect connections. Once your flights are booked, you phone the airline yourself for seat assignments. This worked out just fine for us.
Highly recommend going to www.russiabyriver.com
and ordering the book. A fantastic "companion" for this cruise!