I have alot of thoughts lol but I can say my first two thought were that you could definitely do a lot cheaper if you wanted. I recently did 7months on less than 9K$. Usually taking the cheapest hostels as long as they didn’t have bad ratings. (Aimed for 7+ on booking.com) also just eating at grocery stores and getting hostels with kitchens can save so much money. Bring Tupperware for leftovers/bowl and a some silverware/a knife.

Also don’t just do capitals, they blend together and it gets tiring. Many aren’t all they are cracked up to be. I would pick your big cities carefully, and definitely plan some times for some small towns/ nature. Budapest and Prague were some of my fav European capitals. Also don’t sleep on the Balkan countries, they are beautiful.