Harmonic minor keys are used when writing chords. There is another version of the minor key known as the melodic minor. This is used when writing a melody. Each key signature has two possible keys ...

To fully observe the minor key harmony, the best way to create lines and chord voicings for E7 resolving to the tonic A minor in this key would be to use the notes of A harmonic minor starting on E.

There are various ways to ‘modulate’ to a different key, but one of the easiest is via chromatic modulation - taking a chord in one key and shifting it up one semitone to a chord that’s in the new key ...