Hi,
I just know the Agitato section so I can't really comment on the chord parts at the beginning and end, but I would say that the easiest way to learn the piece is to note that there are certain patterns to pick up. Rachmaninoff will often use the same left hand chords with the right hand parts, so if you see the same shapes come up for the right hand a lot of the time you'll be using the corresponding chords on the left hand with the right.
It's a really fun piece to play though...
