Sounds perfect... the train is certainly a must do. The speed boats/ express ferries are just smaller but just as stable and can go through the narrow fjords.

The Bergen Oslo train itself is quite spectacular. If you go to Flam from Oslo, you can take the ferry to Bergen later in the evening or after an overnight stay. Not many mention this but this combo is certainly the best of both worlds by a distance and you are spot on with your homework.

We were trying to do this but ultimately decided to spend more time in Bergen because of time and didn't regret that; Bergen is lovely. We took a fjord cruise in Bergen.

There is a Nutshell ticket, from oslo to flam by train and flam to bergen by speed boat. Pls let me know that any difference between speed boat and ferry !! and if we go by speed boat, root is same as (via Sognefjord or not) if two options, which one better and enjoyable...

tks

Yes, pretty sure will go through Sognefjord and it won't get dark before midnight so you will have ample daylight to see things in summer... this is probably the best ferry route in the region... enjoy... Cheers!