Telemann’s setting is noted for its clarity and the stylistic bridge it creates between the Baroque and early Classical eras. It is distinct for its remarkably diverse harmonic language.
Pay close attention to the articulation of ornaments within the dense contrapuntal sections.
Brockes Passion, TWV 5:1 is rated Henle level 7 of 9 — late advanced repertoire, roughly ABRSM grade 8 and above. In the RCM system it corresponds to about level 10.
You should be comfortable at Henle level 7 — meaning you can already play level 6–7 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 Brockes Passion, TWV 5:1 lasts about 75 minutes.
Brockes Passion, TWV 5:1 is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.