Telemann's '12 Sonate Metodiche' are didactic works designed to teach systematic approaches to musical expression and technique. They are characterized by their clear structure, melodic charm, and exploration of various compositional devices suitable for instrumental study.
Emphasis should be placed on understanding the melodic and harmonic structures as a guide to interpretation.
12 Sonate Metodiche 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.
12 Sonate Metodiche is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.