I did what you are planning to do, but that was back in 2000, so my experience is much too far in the past to be useful. I did have a wonderful time, traveling mostly by 2nd class Scanrail pass (does it still exist? or was it only for seniors?) but also by Hurtigrute (from Bodo to Stamsund) and by bus in the Lofoten Islands (don't miss those!).

Hostels in the cities require reservations long in advance, and if you want to try unusual ones such as Af Chapman in Stockholm, reserve at least a year ahead. I ended up in a hotel in Stockholm due a foulup at the AYH international reservation office; you are far better off to make reservations with each hostel directly.

Don't expect a language problem; everyone studies English in school and they can even chose British vs. American English. They do appreciate it if you learn a few words of their languages, especially "thank you."