This is a most beautiful prelude, and it is not very difficult (around grade 5), although more difficult than either BWV 939 or 926. The main difficulty (apart form the usual difficulties of hand and finger independence found in cournterpoint music) is the ornamentation. However, this prelude is very efective even if you ommit the ornaments. So I suggest that you learn it first without the ornaments and once it is well ingrained, add them.
BWV 939 (grade 2 – 3) is arguably the easiest of the little preludes, while BWV 926 (around grade 4) is slightly more difficult.
Other little preludes of similar difficulty to BWV 930 you may wish to investigate are:
BWV 924 (grade 4) – the main difficulty is ornamentation, so it will prepare you for similar difficulties on BWV 930.
BWV 927 (grade 4) – fast and fun!
BWV 933 (grade 4) – another energetic, fun prelude.
BWV 925 (grade 5) – A most beautiful little fugue (and my favourite amongst the little preludes) and probably composed by Bach’s son, Wilhelm Friedemann.
BWV 936 (grade 5) – My second favourite, this is a real gem – beautiful three voice piece.
Best wishes,
Bernhard.