It would be very cool. If you go to Finland, know that with the interrail ticket you can get a reduced price on ferries (-20% or smthg).
You should know that booking the train tickets is a pain in some countries (e.g. France, but that's not in your itinerary: there the interrail seats are very limited, very quickly booked, and tickets can be booked earliest 3 months in advance).
If I recall correctly there is a night train going from Berlin to Stockholm through Hamburg and Denmark. That's a nice option.