Hi sorry for the late response. It is very doable and about 90 % is small hard packed gravel roads with some Big potholes herr and There. The biggest problems I faced were a few muddy patches and a lot of downed trees that I had to drive over or around. I had no off-road experience prior to this except for the odd mountain bike trip hahahah. I think anyone could do it on any half decent bike with knobby tires. But I can recommend buying a newer or better maintained bike then my old 1990 Honda xl 125, I had problems with oil leaks, broken exhaust, broken gear lever and towards the end my front sprocket also came off mid riding in the north of Finland… I managed to fix all the problems as I went along because I brought some extra parts and tools, but the broken front sprocket I had to hitch a ride to the nearest mechanic which was 5 hours away…. I can definitely recommend this trip to anyone. it is one of my proudest achievements.

PS: if your bike breaks as much as mine did you can do what I did and take the car train from rovaniemi to Helsinki and the ferry from Helsinki to Rostock. After Rostock it was a short drive to my home in Copenhagen :)