I am a self proclaimed Beethoven master, but utter shite at Mozart, who is my fave. Hammerklavier is difficult, but if you have experiene at beethoven eg 8th, 14th, 23rd sonatas also 19th and 20th, generally considered the easiest it shouldn't be too tricky, especially if you have played liszt. it is quite fun to play but performance is intense and you really need to know the piece super well