Ferdinand Thieriot's 8 Konzertstücke für Orgel Op. 85 are primarily intended for organ, but can be played on piano. They are robust works often with a grand, symphonic character, suitable for liturgical or concert settings.
Focus on projecting a strong, resonant sound and managing the often grand, chordal textures.
8 Kleine Präludien und Fugen 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.
8 Kleine Präludien und Fugen is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.