Liszt's transcription of Mozart's famous choral work is a masterclass in clarity and respectful adaptation. It uniquely preserves the original polyphonic integrity of Mozart while adapting it to the idiomatic capabilities of the piano.
The technical challenge is to maintain strict clarity between the voices, treating it almost as a two-part fugue in certain sections.
Comparable difficulty and character — good candidates for what to learn next.
Ave Verum Corpus de Mozart (S.461a) is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7. In the RCM system it corresponds to about level 7.
You should be comfortable at Henle level 5 — meaning you can already play level 4–5 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 Ave Verum Corpus de Mozart (S.461a) lasts about 3 minutes.
Ave Verum Corpus de Mozart (S.461a) 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 Ave Maria d'Arcadelt by Franz Liszt, Ave Maria (Die Glocken von Rom) by Franz Liszt, Ave Maria after Schubert S558 by Franz Liszt — see the full similar-pieces list on this page.