Your harmony and melodies are the kind of stuff that's right up my alley of interest. Very JRPG-like! I especially enjoy the section from 2:49 to 3:09. :D
I haven't used the Kontakt factory library myself since I'm comfortable with what I have now, but I think you'll find a ton of freedom in familiarizing yourself with the key switch articulations available to you. Making the articulation convincing on instruments goes a long way towards improving the piece, as well as the mix. Personally, I feel that the majority of the mix in an orchestral piece is done in the composing process, where you consider the texture, balance, and function of everything. The whole is greater than the sum of its parts in an orchestra. When things get a bit busier in this song and more voices are involved, it seems like everybody's fighting to be center-stage. Some adjustments to the dynamics of the instruments would really fix this up, especially since not all the instruments are from the same library. They could be all over the place in terms of mic placement, reverb, etc. Giving some dedicated time on individual dynamics can also help to bring some memorable inflection to your melody lines. Your woodwind solos here would stand out a great deal more. On a slightly unrelated note, I also think the pizzicato sounds really unconvincing here, though that's very possibly because of Edirol's limitations (I've never used it myself, so I can't speak for it).
I think you have a pretty good grasp on how to make things sound nice regardless of inexperience with the instrumentation. A little bit of practice and research on the topic should really propel your skills with it forward. :)