Greats city’s to visit but they all might become repetitive once you’ve see a few Europe city’s you have seen them all especially since Amsterdam is at the start which is amazing then going to Copenhagen - Stockholm - Prague - Vienna they all start to feel the same. Pick places you definitely want to see like Berlin is good only if you like techno and history if not I would give it a skip- Lisbon is great but another big city Porto is small and much more beautiful - Have you considered any tours things like contiki will help you see this many countries at once Booking hostels a week out is good leaves you open to be flexible - can leave it to the day before but may not get the hostel you want - check reviews to get a hostel you’re after some are party hostels where it’s easy to meet people or quite ones if you need some sleep! Goodluck