First-time solo traveler going to Europe

Hello, everyone,

I've browsed this sub quite a bit so I have gotten a decent idea of what to expect/do as a solo traveler so what I'm looking for is general things to do in each destination, suggestions for activities/things to bring/random ideas one wouldn't normally think of doing or bringing, which cities require more time in than others to see and do everything, etc. Also, if some cities kind of go against the norm as far as what can be expected (for example, maybe Airbnb is cheaper than a hostel in London or something but hostels are generally cheaper than Airbnb's elsewhere) I'd appreciate that information as well.

The general plan (for now) is flying to Dublin and visiting the city before heading to London, Paris, Berlin and maybe Rome over the course of roughly 4 weeks. Ive been looking at pricing online and it seems cheapest to fly between all those cities as opposed to train or bus (in the case of buses, they're cheaper but they take significantly longer so I figured it was worth the little extra cash).

Thanks for reading, and thanks for any suggestions you all might have!