BWV 676 is a grand and virtuosic prelude and fugue, often referred to as the "Little" Gigue Fugue, though it is in D major. Its energetic character and brilliant passagework make it a significant work in Bach's organ oeuvre.
The rapid passagework and demanding fugal exposition require excellent finger dexterity and stamina.
Allein Gott in der Höh sei Ehr (BWV 676) is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7. In the RCM system it corresponds to about level 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.
A typical performance of Allein Gott in der Höh sei Ehr (BWV 676) lasts about 5 minutes.
Allein Gott in der Höh sei Ehr (BWV 676) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.