Feedback on a NIN itinerary

Seems that you will share Flam with a few thousand cruise passengers:
https://www.flamport.no/arrival-list

Yes, I know. I wish I'd looked at that before I booked our flights.

Your plan falls at the first hurdle, which has nothing whatsoever to do with cruise passengers.

The only Norled boat from Flam to Balestrand leaves at 1530.

Given that the first train from Oslo arrives at Flam at after 1pm the plan is a physical impossibility.

As it happens the 1206 train connection from Myrdal (off the 0625 from Oslo) is sold out. That has as much to do with the Norway in a Nutshell people as with cruise passengers. Thus you need to book this as two tickets and forget the valley bike ride -
0625 Oslo to Myrdal, wait there for 2 hours then the 1324 train to Flam, arrive 1422, then boat as above.

Now if you left your main luggage in Oslo and travelled light, you could cycle down the valley rather than wait for the train.

The only Balestrand to Flam boat is at 1158, arrive 1340. Then the 1500 Nutshell special boat.

The bus from Gudvangen to Voss and train Voss to Bergen don't have to be pre booked- the train is a commuter train.

Note that there is also an 0750 Norled boat direct from Balestrand to Bergen arrive 1150.
Rather than fly back to Bergen you could take the 0704 train/bus to Gudvangen, the 1100 Lustrabattane boat to Flam and the 1330 train to Oslo.
That train is beaten into Oslo by the 1425 bus from Flam.

Note that there is also an 0940 bus from Oslo to Balestrand connecting at Sogndal.

However you do this Bergen gets half a day, way too short.

Thank you for all your information. I'm now wondering if I can do our trip in reverse. Flight to Bergen on day 1, spend day 2 in Bergen and head for Basestrand on Tues, keep my hotels in Balestrand. If we took the ferry from Bergen straight to Balestrand, do we miss much from the NIN train/bus route? We would be in Flam on day 5 when there are still cruise ship passengers, but not quite as many. Our flight out of Oslo is at 20:15, so we would have about one day in Oslo, part of day 5 and most of day 6. What is the website to look at the ferry schedule?

https://www.norled.no/wp-content/uploads/2024/11/572854be-e680-4dda-9d16-e5f0382f6456.pdf

https://en.lustrabaatane.no/flam-gudvangen

The basic problem is trying to fit the Gudvangen to Flam fjord cruise into this. A key part of the itinerary. You probably could more easily when there was the long gone Oslo to Flam night train.
So the way to do it is leave Bergen for Flam at 0704, change to bus #450 at Voss, arrive Flam at 0926.
Leave Flam for Gudvangen on the Lustrabattane boat at 1100, arrive 1300, depart from the E16 junction Gudvangen on Bus #450 at 1351, arrive Flam 1411 in good time for the Balestrand boat.
Day 5- Balestrand to Flam then the 1615 train to Oslo, arrive 2304.

An interesting timetable challenge.

Balestrand is by all accounts a pleasant town to stay in, but there is a reason Rick doesn't recommend it as a base on a Nutshell trip unless you have more than 2 nights in the area (I think that's what he says; I'm traveling and don't have access to my notes). That reason would be logistics. The NiN segments are on the south side of the Sognefjord. Balestrand is on the north side of the Sognefjord. Ferries between Balestrand and Flam are extremely infrequent.

I did a lot of research before my 2023 trip to Norway. I am satisfied that substituting the express boat between Balestrand and Bergen for the Naeroyfjord ferry (Flam-Gudvangen) and/or the Flamsbana (Myrdal-Flam) is a poor trade-off. The part of the Sognefjord traversed by the Balestrand-Bergen express boat is much wider than the Naeroyfjord, so the express boat doesn't give you the expected fjord experience.