Preparatory pieces for Sibelius' Romance, Kreisleriana #8 and Polichinelle

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I have been eyeing the following pieces for a while:

Sibelius - Romance op 24 no 9
Schumann - Kreisleriana no 8
Rachmaninoff - Polichinelle

It would be rather pointless to tackle them straight away, as I am not technically advanced enough for it to be worth it. Which pieces would be good preparation for them? Something around level 5 until the actual level of the piece.

Something with extensive octave and scales HT in Dm would likely be useful for the romance, but I do not know of any easy pieces which cover these extensively.

Any help would be appreciated, thanks!