Raff's '10 Gesänge für gemischten Chor' Op.198 are settings of vocal pieces for mixed choir, showcasing his skill in composing for vocal ensembles. The piano arrangements would likely emphasize rich harmonic textures and a sense of grandeur.
10 Gesänge für gemischten Chor (Op.198) 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.
10 Gesänge für gemischten Chor (Op.198) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.