Bergen to Tromso

Hi
We have 3 weeks in July / August and would like to travel from Bergen towards Tromso (maybe not getting that far) without booking ferries, just moving on as we feel like it.
My question is - do we need to book all the ferry travel ahead of time or can we just turn up? We won't necessarily need a cabin but if it is an overnight trip that would be nice.

Also we'd like to book a self-catering cottage somewhere en route for a week? Any suggestions?

Any advice??
Thanks

By the ferry, do you mean the Hertigruten Cruise ships?

With the sole exception of the long-haul Hurtigruten passenger/tourist ships, there are no domestic overnight ferries (and thus no cabins) anywhere in Norway. As for regular passenger/car ferries, it's not necessary (and may not even be possible) to pre-book: just turn up and stand in line. At major crossing points you may have to factor in some waiting time, especially given the fact you're travelling in high season, but most of the time things run relatively smoothly.

The cottage question largely depends on what kind of activities you want to engage in whilst staying in aforementioned cottage. A little more info, please?

W.