In-depth review for you, my friend.
I think you've done a great job in the composition side considering your goal. It fits perfectly into the style you set out for.
You wanted feedback on mixing so here's what I think.
Your instruments need to each have more "identity" in the mix, they need to find their own spaces in order to make the piece shine. For example, the track is quite muddy, around 300 to 400hz there's a lot going on and it would benefit from a few instruments being moved away from that area. The brass would benefit from a boost in the mids (1000hz) and I would take a little away from the 400hz area at the same time.
The percussion sounds weak, unenthusiastic. By fixing the mix the percussion should come out more, helping to bring out the "boom", the resonance from hitting a drum. If it doesn't, allow the drums to take up more of the low-mids. The percussion's transients are quite good already (the first sound made, where the drum is hit, is the transient).
In general I think the piece needs more high frequencies too, more "bite" or "shine" (giving you the mixing terms there).
You did use the stereo spectrum well though, it's wide and the instruments sound authentic too, which is a bonus.
I'll send you a PM with some more stuff. :)