You know, I've listened to this several times now. I really wish I could offer some type of advice or critique, and even though it's hard to do so when I know there are more movements to come, I still wish I could. I don't play violin, or any orchestral instrument for that matter, so I'm glad there are at least a few violinists that can share their thoughts on a piece meant to place it at the forefront.
I've dabbled with quartal and quintal harmonies before, but to me they've become a device I use in composing, rather than a structural component building the actual overall harmony. It's fascinating to hear how masterfully you wield it. It's a beautiful dissonance maybe one day I'll understand more.
However, just because it's foreign to me doesn't mean I don't appreciate the beauty of it. I'm not a physicist, yet I'm in awe of the James Webb photos recently taken. I'm not super into metal music, but that doesn't mean I don't love what Meshuggah and Vildhjarta bring to music. I'm someone who appreciates all kinds of music and art, and I think it speaks volumes for your music that you're able to reach people like me; even though this isn't a style I would write in, I absolutely love your musical voice.
I'm a fan of the sparse orchestration. I think it would be a hindrance for you to try and create lush gigantic harmonies with such yearning thematic material. I did like the ending of the moderato assai section, I felt like it needed a bit of girth near the end.
I'm excited to hear more of this, and it's fantastic for you to be able to work with the violinist as well. I'm sure you learned a lot by conferring with him/her; how great for you as a composer! Will there be a recording of this piece?
Absolute fantastic piece you have here, and I'm excited to hear how you revise this as well as the next movements. Keep us updated, and thanks for sharing!