Mixing and sound design isn't my area, but I can say the composition is nice! You might experiment with varying the harmonic presentation occasionally to spice up the sections where there isn't as much happening in terms of melodic lines. For example, arpeggios/voicing/instrumentation, etc. Just a thought, but really it's quite a well thought out piece, keep it up!
p.s. now that I'm listening a second time, I hear that you did what I just mentioned! It's a little hard to dig out of all the sounds going on. It's so cool, find a way to spotlight it! :)
Unless the piece is notably aleatoric, I would suggest some sort of closure for most instruments, as a general rule. Definitely not always. It doesn't even have to be that audible.
When I applied to conservatories for comp before I switched to Music Education, they were very picky about classical theory and orchestration, and then ideas. That's all I can say, considering I don't know if you really like this piece or if it's an example of your best work.
That makes sense, it's about the performers then, not the instruments? In that case, should all instruments have closure, and was it just a case that you picked up on it for the winds? Ah, I'll fix the sixteenth, rest figure.
Thanks very much.
P.S I'm currently putting together a portfolio for conservatoires for entry to undergraduate composition courses. Do you think this would be a suitable submission?