• Which note is right hand, which is left? I mean not as a technical problem to play, but to listen to. What notes do you hear as being the melody?
Listen to the file and concentrate on the left hand by following the sheet. (From measure 271 it's more easy to hear). And than the same with the right hand. The red notes are the same in the left and the right.
On the sheet I choosed to place them in the left hand part. Because of the pattern. And because it is that way when the right hand goes an octave up in measure 272.

This reminds me of looking at pictures of the magic eye book: 'the picture can be seen different depending on how you concentrate' = 'the notes can be heard different (melody or accompaniment) depending on how you concentrate'.

• I use an eight note and rest instead of a quarter note because of the lay out. Otherwise I need to enlarge the measures and use more pages.
The b fits better above the rest than above the eight note: