Johann Baptist Cramer's Op. 9 sonatas are pedagogically significant, often focusing on specific technical challenges within their Classical framework. They balance melodic grace with demands for dexterity.
Practice the independent movement of the left hand while maintaining melodic clarity in the right.
3 Piano Sonatas (Op.9) is rated Henle level 4 of 9 — intermediate repertoire, roughly ABRSM grades 5–6. In the RCM system it corresponds to about level 5.
You should be comfortable at Henle level 4 — meaning you can already play level 3–4 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 3 Piano Sonatas (Op.9) lasts about 20 minutes.
3 Piano Sonatas (Op.9) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.