What is a correct sequence of notes in Chopin's Prelude #8 when playing slowly? How should 32nds be played against a triplet of 16ths plus and 8th? It seems that there are no together played notes in both hands like some tutorials advise (except the first). Should it be played like together-right hand-left-right-right-left-right-right-left-right-right, or how?
There are, but that's not the point of this piece.
As long as you play this prelude slowly enough that you can distinguish these cases, it's way too slow for the intended effect. Once you've managed to reach the proper agitato speed, all that matters is that the first note of each beat should be simultaneous for both hands, and the second large note of the right should come after the lowest bass note. The small notes have to be as fast as possible in order to fit between those notes at all. Neither the player nor the listener will be able to perceive the exact timing between those notes anyway; the effect to achieve is that of a haze of chord notes.
(If you examine the score mathematically, you'll see that there are two more simultaneous notes in each beat: the lower bass note and the 5th demisemiquaver. But as noted, the point is not to hear this; if you can, it's not agitato!)
The passage should be played as follows:
T = together L = left hand R = right hand first half-beat // second half-beat T R L R L R // T R R R
X:1 T:Chopin Prelude in F# Minor T:Order of notes K:F#min M:C L:1/32 [V:RH] "_T"C"_R"c"_R"G"_R"B"_T"A"_R"F"_R"D"_R"d [V:LH clef=bass middle=d] (3"^T"a2"^L"c2"^L"f2"^T"F4
For this and an excellent approach to practicing the piece, see "A Pedagogical Approach to Technique in Chopin's Preludes Op. 28" (Sheila Kay Barnhart, 2014, Ph.D. diss, West Virginia University, pp. 41-45).