Johann Baptist Cramer's '4 Waltzes' are instructive pieces that, while serving a pedagogical purpose, also offer charming musical moments with clear Classical era sensibilities.
Focus on clean articulation and a light touch to capture the elegant character of these early waltzes.
4 Waltzes is rated Henle level 4 of 9 — intermediate repertoire, roughly ABRSM grades 5–6. In the RCM system it corresponds to about level 4.
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.
4 Waltzes is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.