Help w La Campanella

[gimmethedeetz]

I hope this is the right place to post this... I am trying my hand at La Campanella, and as expected it is taking weeks to learn.
1- I wanted to ask some advice on the best way to go about learning the song - i played for years as a child recreationally, never professionally, am taking a few lines at a time, hands separately, hands together and slowly speeding up. this is all for fun, no time limit etc. Is there a better way to do this?

2- specifically, wanted to ask about this measure -
Why specify the D double sharp here and then an E later in the measure? Why not just an E in the first place? Am I just missing something blatantly obvious?