For Eastern Europe I think you would like the following.
Beaches - Croatia for places on the Adriatic Sea or Bulgaria for the Black Sea
For meeting people to chill with, this could be anywhere. I have not had a problem meeting anyone at hostels.
Music - In any of the major Eastern Europe cities, you will find places that have the type of music you are looking for. You might want to check online for Open Air Festivals, which are usually three days concerts held outside of a city that can have 50-75 bands. They have a lot that are metal only, but also other genres and also some that are just a mix of many genres.
Taking Pictures and Videos - I think Prague is the most beautiful city in Eastern Europe and you will get a lot of quality shots here. Also, Budapest and Krakow are very nice.
To see new things and cultures, how about some of the lesser travelled Baltic countries? These could include Serbia, Bosnia, Albania, and FYR Macedonia.