Wow, this is really beautiful music.
A couple quick notes before I get into it:
-make sure the double basses have a C extension for measure 5
-I liked the sustained flute notes in the introduction. What if you had continuous lines for them and they alternated when to breathe?
-Pizz notes were very hard to hear starting at bar 66, but that could be because of the transition to the better samples
-I would have tried to do something a bit different than having all the low string playing triplets, but eh that's just me and a preference thing
Now, onto the music. I absolutely LOVE the harmony you create. There were several moments the chords fell onto a diminished chord, or the subtle rising chromatic parts, that really pulled my heart strings. I normally listen to a piece several times while commenting, but found myself wanting to hear this one again and again because I like it so much.
Yeah, the middle fast section seemed a bit abrupt, but it was really cool. It sounds like you were under a time constraint? Regardless, if your plan is to expand this one into a larger symphonic work, I would for sure elongate that entire section. You have plenty of material to craft really cool motifs from the string lines, just give them a bit of rhythm and a cadence so you can really toy around with it. If it were me, I'd keep the first introduction section as is (really great English horn stuff there), and develop the crap out of the middle section. Maybe make that your main theme, or possibly even get two themes out of it for a sonata-allegro form. Dunno, the gears were turning listening to this piece. You could even have your return to the slower adagio material be a brief interlude before going back to some faster moments for a recapitulation.
Ooh, ooh, what if you made the English horn as a feature for the introduction and slower return, really highlighting how beautiful the solo lines you gave it are? (I just really like the instrument 😄)
Another idea I had would be an extended use of the percussion. I know you're going for the classical orchestra type of vibe, but the timpani was a part where I thought you could explore more as you develop this piece. Even giving it rhythms and ostinatos during the fast section would be cool. It's just too much I hear it used as if Beethoven were using it. But a LOT of rhythmic exploration and development has happened since his time, I think it would be cool if you explored some of it's possibilities. Some of Shostakovich's music comes to mind as I type this, kind of a classical yet modern take on it (at least for his day, who knows what you could come up with!)
Obviously this all depends on what you're going for, these were just some thoughts that came to mind as I listened. I really like all the slower romantic sections, some of the solo melodies you created were wonderful, and your use of harmony was very touching. Keep us all updated on how this one turns out, I'm eager to hear it 🙂