Telemann's '12 Methodic Sonatas' are excellent examples of Baroque instrumental writing, designed for pedagogical purposes while remaining musically engaging. They feature clear melodic lines and contrapuntal textures.
Focus on precise articulation and the clear delineation of melodic and contrapuntal lines.
12 Methodic Sonatas is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7. In the RCM system it corresponds to about level 5.
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.
A typical performance of 12 Methodic Sonatas lasts about 40 minutes.
12 Methodic Sonatas is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.