I should call you extremely reckless for spending all that money on those samples without first having at least a few years of struggling up through some starter sample libraries and a few dozen works, but this is very very well written and shows a lot of experience for a "first piece" so I can't say that. :P
Excellent motion and feel in this. You have a great ear for ideal dynamics and orchestration. I would be shocked if you haven't at least studied composition and orchestration for a few years and/or been under a mentor.
The only shaky transition I see is at 1:59. It's just too sudden. I'd use the 60" gong from EWQL SO with a mid-volume hit to just "whooosh" that through.
You remind me a lot of myself- you have a lot of ideas, and you try to cram them into one piece because you're in a state of "oh man, this is awesome, I know what should go next!"
The motif at 3:16 with the trumpet being doubled by horn should also be doubled two octaves below or such by trombones or tuba. Make that one bad ass tutti.
In general, this piece reminds me a lot of the fantastic score to How to Train Your Dragon, which won an award I believe. Give it a listen if you haven't already.
Let me know if you're ever interested in collaborating. You have a very good sound and lots of great ideas.