First time solo

Hi all, I’ve had a great time looking through everyone’s post and thought it would be good to pick up some tips for a first time solo traveler. I’m 20m, from Wales and planning on going around Europe for around 3 weeks in August. I’ve got an idea of some of the main places I want to visit such as Berlin, Wroclaw, Prague and Budapest with my main interests being nightlife, hiking and meeting people. My budget is around £2000-£2500 but it doesn’t really matter if I go over

One place that i’m interested in is Vienna as its on the way in my route. Is there much to do in terms or cool places to see and places to meet people? is there any other places around there that is good for hiking? Id love to hear any other suggestions around my planned routes.

I’m planning on going budget by using hostels and Flixbus. Is there anywhere that I may have missed that would match my interest? if so, I’d love to hear. I’m also trying to decide how long id like to spend in each place.

I’m also planning on going with the flow while in there and not booking everything before leaving . Is this a sensible choice or would it be much better pre booking accommodation etc?

Any advice whatsoever is greatly appreciated :)

First time solo