For bar 30 in the G minor, I only use one hand. However, as long as you can play fluidly (so there's no break or unevenness between hands), using both hands is fine.
33-1 (f minor) isn't particularly difficult note-wise once you've got it in your hands. However, be careful with pedalling - you want the top voice to ring out though the duration of every measure, and if you use too much pedalling the accompanying chords will drown out the melody. Can't think of any other specific troubles that might arise from it.
33-3 (C minor) I take back what I said for this one - since I last posted, I came to the conclusion that it's an amazing piece.
The difficulty here also lies in the voicing. Make sure you don't lose the melody with all the 16th notes which reach far above the melody itself. Though you can do neat things with stressing the 16th notes, but always make sure to listen to yourself so the melody doesn't fade away.
The break in numbers might be due to Rachmaninoff's numbering. He removed three etudes from this set, and put two of them back later. So the ordering is sometimes odd.
33-4 (D minor) This is possibly MY favorite etude. I would say it's rather difficult, as it requires a great deal of care to shape a beautiful sound. Furthermore, there are more "voices" than would be apparent only by looking at the stems of the notes. For example, if you look at measure 11, that section has four voices, and it's quite a challenge to bring each of them out. It gets harder later on, but you still have hidden little melodies and voices which aren't marked. I don't know if Rachmaninoff wrote the piece with extra melodies in mind, but they are certainly there, and he probably did know what he was doing with composing at this point.
I gotta run, I'll finish this up later. Good luck!
Topic: Etudes Tableaux- Recordings