In key of C minor (Eb Major) for the first 8 bars and last 4 bars - harmonized:
i - Cmin7
ii* - Dmin7b5
III - Ebmaj7
iv - Fmin7
v - Gmin7(b9) (The third is raised from Bb to B so that it becomes G7(alt) - a 'Harmonic Minor' cadence)
VI - Abmaj7#11
VII - Bb7

Then in key of Db major - harmonized:
I - Dbmaj7
ii - Ebmin7
iii - Fmin7(b9)
IV - Gbmaj7#11
V - Ab7
vi - Bbmin7
vii* - Cmin7b5

C Minor:
	i	i	iv	iv(VII)
	ii*	V	i	i		<< Spot the 2/5/1 progression

Db Major:
	ii	V	I	I		<< Spot the 2/5/1 progression

C Minor:
	ii*	V	i	i		<< That fourth and final i chord (Cmin7) could be replaced by a Dmin7b5/G7 turnaround

Try some tritone substitution on those V chords (Dmin7b5 Db? Cmin7 and Ebmin7 D7? Dbmaj7)!

Try some backcyling through circle of fourths/fifths (Cmin7's fourth/fifth is Fmin7, maybe try Dbmaj7's fourth/fifth Gbmaj#11 - or even multiple cycles such as Bb/F/C or D/G/C?)!

If you have a backcyle from 5>1 you can always use tritone substituion on that 'artificial' reharmonisation! E.g. rather than A>D try Eb>D.

Chord qualities in reharmonisations should be derived from what sounds best/justified against the melody notes - nothing else!

A dominant 7th chord can be followed by it's parallel minor chord - e.g. go from F7 to Fmin7, where Fmin7 is the target chord to land on.

You could reharmonise the minor 2>5 cadence (Dmin7b5>G7alt) to a b6>V (Abmaj7#11>G7alt)

Notice how most of the piece moves in fourths.

The Ebmin7 Ab7 Dbmaj7/Dmin7b5 G7 could sort-of be looked at as a 3 6 2 5 (very common progression/turnaround) in the key of C minor - NOTE: this could be played as Ebmin7 Ab7 Dmin7b5 G7alt OR diatonically in key of C minor as Ebmaj7 (Ionian) Abmaj7#11 (Lydian) Dmin7b5 G7alt.