While Bach wrote extensively for solo keyboard, a collection titled '7 Stücke für Streichorchester' is unusual and might refer to arrangements or transcriptions. If indeed for strings, it would showcase Bach's masterful contrapuntal writing and harmonic depth.
The main technical challenge, assuming it's an arrangement, would be to capture the clarity of contrapuntal lines and orchestral textures on the piano.
7 Stücke für Streichorchester is rated Henle level 6 of 9 — advanced repertoire, roughly ABRSM grades 7–8. In the RCM system it corresponds to about level 9.
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.
7 Stücke für Streichorchester is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.