Difficulty, used in rating sense, is very subjective I know, but I picked up from those threads that No 3 ranks as the 2nd (maybe 3rd) most difficult Scherzo of the four found outside of the Sonata form.
So my question is regarding where the difficulties are found, including the part that would be considered most difficult.
Chopin wrote four Scherzi.
I've answered this exact question twice on the forum. The descending pianissimo eight-note figures, starting on page four, are the most difficult part of this piece.
If you have any specific questions feel free to ask them - there are maybe a hundred people on this fourm who've played this piece and are willing to help you.