A composition for an organ that incorporates a hymn tune is known as a chorale prelude.

Take your pick! Extant forms when Bach began composing included the Prelude, the Fugue, the Chorale Prelude, the Toccata, several concertante forms, and so on. Bach raised all of them to their highest peak. There is no one best answer, but the "safe" answer is probably "Chorale Prelude".

A minor

N. van Hichtum has written:

'Der wie ris in ald wyfke'

Jochen Schimmang has written:

'Der Norden leuchtet'