re: How long should you stay in cities while backpacking?

I would highly recommend removing Stockholm and Oslo from your list. They are very expensive and out of your way. Unless you REALLY want to go there. But the problem is you have to get there and basically come straight back. So you can't even really tie it into your trip.

Try not to take flights. The way you keep backpacking cheap is by short cheap train rides. Getting to and from Airports can be expensive. There's more to a flight than just the cost of the flights. Train stations are usually close to the city centers, you basically get there and get on the train with almost no additional costs. Flights are also more mentally exhausting to me. Going through security, arriving on time, planning it out, etc. Trains are so nice because you just arrive, walk on, and go.

I also can't recommend some time outside of the main cities also. Some of my best European memories are from the country and small towns. I say on this board all the time, hitting the big cities is like getting a taste of Louisiana by only going to downtown NOLA.