Train from Oslo to Bergen, Norway

My friend and I ( semi-retired ladies) are taking a 12 days cruise of Norwegian Fiords on Hertigruten Line starting Sept. 19. We are arriving in Oslo already on the 12th. We would like to see Oslo in 2 days, then spend 3 days travelling to Bergen and have two questions: 1) Please advise on the best arrangments for the famous train from Oslo to Bergen and where to stay overnight 2) If you taken that cruise please reccomend which land trips to add and which harbors to see. Any suggestions will be most appreciated. Thank you, Zofia