Yes-Bod/o and Narvik you can see´do´ in 1 - 2 hrs-there is nothing (they are actually small villages for germans-maybe 5/10.000 people). Using that ´fast=hastig/hurtig´ boat is very costly and there is also a BUS Narvik-Hammerfest-KIrkenes.

You also make a long and unneeded detour via SE south -then up north again. Rearrange that. OR use any of the many more ferries going over Botnia (but these may freeze out in winter) from SE-FI.

Narvik -if you really want to ´see’it-the short stop on the boat is enough-then head south from Nordkappen by bus via FI (cheaper) or SE to Rovaniemi/Kiruna or whatever and plan from there.

OH-and this is just personal-but if you are of older age-visit the ABBA museum in STO (its strange to have a msm for still living people, but its more of an experience centre)

Check when the Swedes and Finns do their usual earlyspring/latewinter/holidays-many routes then will be swamped with skiers.

Trains. Compulsory reservations from Oslo to Bergen and Trondheim and Bodo. I advise reservations Hamburg to Copenhagen as these trains have very small capacity.
The boat is expensive and it doesn’t go to the tip of Northcape. They offer an excursion there at additional charge. It doesn’t go to Narvik anyway.

The only thing at Bodo is the air museum. There’s nothing at Narvik for a tourist but there is a sleeper train to Stockholm. Reservations required.

I can’t advise about Finland. Scandinavia is very expensive compared to the rest of Europe so plan carefully. It will be cold with long nights