J.S. Bach's '2 Sonaten und eine Fuge' from the set BWV 954 is a prime example of his mastery of counterpoint and thematic development in the Baroque era. The sonatas often feature clear melodic lines and solid harmonic structure, leading into a complex fugue.
Developing the ability to clearly articulate each contrapuntal line and maintain rhythmic integrity throughout the fugue are the primary technical hurdles.
2 Sonaten und eine Fuge, 954 is rated Henle level 6 of 9 — advanced repertoire, roughly ABRSM grades 7–8. In the RCM system it corresponds to about level 8.
You should be comfortable at Henle level 6 — meaning you can already play level 5–6 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 2 Sonaten und eine Fuge, 954 lasts about 10 minutes.
2 Sonaten und eine Fuge, 954 is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.