Busoni's cadenza displays his unique harmonic sensibility applied to the works of Mozart. It transforms the classical structure into a more dense, late-Romantic tapestry.
The focus should be on maintaining a refined, Mozartian character while managing the complex, often chromatic inner voices added by Busoni.
Comparable difficulty and character — good candidates for what to learn next.
Cadenza to Mozart's Piano Concerto, BV B 10 is rated Henle level 8 of 9 — concert repertoire, roughly diploma level.
You should be comfortable at Henle level 8 — meaning you can already play level 7–8 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
A typical performance of Cadenza to Mozart's Piano Concerto, BV B 10 lasts about 2 minutes.
Cadenza to Mozart's Piano Concerto, BV B 10 is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.
Pieces at a comparable difficulty and character include Cadenza to Mozart's Piano Concerto No.23, BV B 9 by Ferruccio Busoni, Cadenza to Mozart's Piano Concerto No. 23 by Ferruccio Busoni, Canonic Variations & Fugue in C Minor by Ferruccio Busoni — see the full similar-pieces list on this page.