Help with String Quintet

Hello, I'm new to this site. I only got into music about 3 years ago (I'm 19 now) and I need help because this is my first composition. So I understand most musical jargon, but I'm wanting to study Composition next year at a Music Conservatorium. Constructive feedback would be awesome! I know the piece isn't perfect which is why I need help!

Do you want criticism as though a college professor was critiquing your work? While I'm not a professor, I do teach composition and theory sometimes. 

Yeah, although remember this is my first composition. I understand I have a lot to learn which is why I want to study composition at a University level. So without too much negativity, constructively tell me what I should do to improve it! 

• Consideration of bowings: Most of your notes seem like they don't consider the bow directions of the players, and generally lack slurs. which, in addition to making the performance more potentially emotional, could fix the problem of direction. In m. 21 for example, you have the rhythmic ostinato end on a dotted half note before continuing, which makes the bass and 'cello awkwardly start the pattern on an up bow the next time. This is echoed sometimes in your melodic or homophonically written parts.
• Crossed voices: For seemingly unnecessary reasons, you have the vocal structure or the melodic of homophonic lines of your parts overlap each other measure to measure. mm. 13-14 is a prime example of this. It's a little bit confusing to hear where the melody is the dominant part constantly shifts with no help from the dynamic markings to clear up where we should listen to. This is especially a problem when the ostinato in the cello cross-voices with the melodic parts, since the quicker it happens, the less clear the parts sound.
• Conventional: "arco" should be not capitalized and should not have a period after it. "pizz" should be not capitalized and should have a period after it, since it is an abbreviation. The cello should not get a pp marking until its first note. 
• Doubling: Doubling the cello and bass for that long with the exception of some notes makes for relatively weak orchestration. Doesn't give much in terms of sonically increasing the pallet especially since there's only 5 players; you're going to want to use all of them to the best ability instead of constantly doubling them, especially since they're 2 octaves apart, instead of one.
• Chord progressions: They're all rather short and a lot of them seem to end on the tonic or dominant, and don't stray away from that too much... 4 bar phrases work, but the drama increases with more tension created by harmonic systems, multitonics especially in altered tone scenarios like this, and just general unfamiliarity with something will resonate within an audience more. The chromatic line you establish is good, but it really just needs to go further. Use a VI chord with the ostinato starting on the 5th, or a III chord with the ostinato starting on the tonic, or anything to mix it up a little bit. 
• Dynamics: Your dynamic markings seem to be a little inconsistent. Like, one line will get a dim. and the other one that plays the same if not something similar will not. This continues until the end of the piece. I know it's annoying to mark every part, but it's expected.

Overall, you have some good ideas in here; the melodic rhythm is interesting and you stay away from the "lowest note gets the tonic" rule a lot of beginner composers fall into. However, it just needs more, both in terms of length and in terms of motion, harmonically and dramatically speaking.