At the end of the day, I guess I'm not a very good purely electronic composer lol. I think the biggest limitation I was facing was the fact that you can't easily change the gate length with modular and as a result it gets very same-y to my ears.
So, voice-wise, I went to my small MIDI setup and sync'd it up to the modular, which is easily done via the Erica Synths MIDI <-> CLK module. This now adds a second sequencer (MC-500) and palette of sustainable sounds.
Revisiting the first Subject, I kept the original key and tempo (Dm, 88 bpm) and started working on a new motive. I ended up on a solo cello patch on the JV Orchestral expansion card playing a sparse melody in D Pentatonic Minor. After it plays the motive the first time it's harmonized by a second cello line outlining the chords of Dm-C-Dm.

As you can see, the melody line has been stripped back to the most minimal I could make it whilst still keeping it moving forward. It sustains on each of the chord tones in Dm to reinforce Dm as the i chord.
And so far, so good! The build is slow I'm working really hard to make each additional voice really add something to the overall composition. How successful I will be remains to be seen! :D