This is really beautiful writing. I know it's not in fifths but the opening reminded me a lot of the opening of "Daphnis and Chloe" the way you opened with chords that sounded like dissonance but resolves without having to actually change. I was hooked from the beginning! I'm going to be honest, since I use a non-compatible browser, I was able to get through most of the piece before it reset itself but I was able to hear the rest in my head, so just a heads up.
A lot of really awesome resolutions to half-diminshed chords. I wish there was a name for this, because it's always so eerie and interesting wherever it happens. In particular, I like the E half-diminished you first have in your winds, then your strings, in m. 36. "Prelude to the Afternoon of a Fawn" is the piece I heard there (talk about French influence!).
Your wind writing, despite it not having some welcomed breath marks in it, sounds amazing and was a perfect little flurry atop the rest of the orchestra, especially in the beginning. Well done.
The conductor/teacher side of me is just picky about your engraving! In your strings, sometimes the cellos and basses could have been in higher clefs, and the staves could have been dragged down to accommodate for both notes and slurs. Same goes for the winds, but just for the slurs. Seeing them cross staves like that gets kind of obnoxious for conductors looking at these pieces for the first time.
But really, that's just a spacing issue that doesn't comment on the piece. The rest was gorgeous, and MIDI doesn't do it enough justice! Hope to hear more!