Hey Nicolas, thanks for sharing your work with us. Great job on completing a piece of such a large scale! I like how fluid your embellishments are within parts of the chord. However, it does not look good on paper and I have some other questions and suggestions for you as well:
Your instrument list indicates 2 alto flutes, but there's only one part to be played throughout the manuscript. This second alto flute player could be swapped to a Piccolo player because I noticed you have the flutes playing above a high A in some places. While not impossible for an experienced flute player, it is highly unstable and they will not be able to sustain it 9 times out of 10. Especially that high D flat around 4'24" in the first movement.
You also note in your description that there are only 2 Horns in F while there are sometimes more than 3 notes in the sheet music. I would highly suggest using 4 horns on two separate staffs as it gives you more depth and force if needed.
The manuscript you provided is in concert pitch. It might not bug other people, but it bugs me immensely. There are WAY too many ledger lines in some of these parts. The instruments' ranges that are not tuned in concert pitch tend to line up on the staff very nicely and do not require so many ledger lines. The Horns in F should be in treble clef - the performers should not be reading ledger lines above the bass clef.
The manuscript does not indicate a2 or divisi in any part.
You desire to expand these instruments' boundaries and capabilities, but some of the things you are asking for are just not possible. If you're going to write for such a large orchestra and plan to write very difficult music, then you need to meet the challenge and study scores of some of the great orchestrators - Ravel, Mahler, Liszt, Bruckner, Scriabin, Holst, and many more.
I'm leaving 2 links underneath that are great references to use when questions about notation and instruments arise. These books are massively beneficial to contemporary orchestrators and composers.
https://www.amazon.com/Essential-Dictionary-Music-Notation-Pocket/dp/0882847309
https://a.co/d/0dPZYay
Thank you again for sharing your music. I hope these comments find you well and that you do not take offense to them as that was not the intention.