These are transcriptions of Schubert's beloved melodies, adapted for the harmonium. The focus will be on capturing the warmth and emotional depth of Schubert's writing through the sustained tones of the harmonium.
Maintaining a singing tone and subtle dynamic shaping for each melody is key.
32 Mélodies transcrites pour harmonium is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7.
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.
32 Mélodies transcrites pour harmonium is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.