Based on a Gregorian chant, this piece is one of Liszt's more austere and harmonically adventurous transcriptions. It creates a vast soundscape through simple melodic motifs and shifting tonal centers.
The technical difficulty lies in voicing the chant melody clearly through thicker harmonic textures.
Comparable difficulty and character — good candidates for what to learn next.
Ave maris stella (S.506) is rated Henle level 7 of 9 — late advanced repertoire, roughly ABRSM grade 8 and above. In the RCM system it corresponds to about level 9.
You should be comfortable at Henle level 7 — meaning you can already play level 6–7 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 maris stella (S.506) lasts about 5 minutes.
Ave maris stella (S.506) 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 maris stella, Solo piano by Franz Liszt, Bénédiction de Dieu dans la solitude by Franz Liszt, Cantico del sol di Francesco d'Assisi by Franz Liszt — see the full similar-pieces list on this page.