Cramer's preludes are widely recognized pedagogical works, serving as excellent studies for developing foundational piano technique. They are characterized by their clarity and musicality.
Focus on developing evenness of tone and finger control in various articulations.
26 Préludes is rated Henle level 4 of 9 — intermediate repertoire, roughly ABRSM grades 5–6. In the RCM system it corresponds to about level 7.
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.
26 Préludes is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.