There's a lot to read below and I don't want you to get discouraged by it. You're off to a very good start! You have good materials which are readily accessible for concert band. Polish this up and it could be widely playable.
That said, here are my concerns about the piece and some advice on fixing them:
1. Too much material too soon: I'm still getting to know the theme (glockenspiel, m. 1-4) when I suddenly have to pay attention to two rhythmically active new planes in m. 3 (Fl. 1/Cl. 1 and Bsn/Trb. 1). As a composer, you have to remember that only you are intimately familiar with your materials. Always assume your audience is hearing the piece for the first time.
In this case, for example, I think you could actually expand the first four bars into 8 bars, stating your theme first then layering in the 8th note counter line while repeating the theme. Save the syncopated figure in the low brass and winds for later in the piece. It would be a really useful intensifier as you grow the texture.
2. Undefined planes of sound: The key concept of composing for large ensembles is using planes of sound to create definition in the sound space. Using the beginning of your piece as an example, the Glockenspiel and Flute 2 form a coherent plane of sound. They say the same thing rhythmically at the same time and it's clearly differentiated from what else is happening (except for the 8th note offset between the parts in m.3). Likewise, Piccolo and Clarinet 1 form a coherent plane of sound in m. 3-4 with the 8th note idea. Clarinet 2 in m. 3-4 muddies the sound space by jumping from one plane to another. Switching instruments between planes of sound can be useful when done deliberately, but care should be taken.
The trombone figure in m. 3 also muddies the sound space because it is so rhythmically close to the 8th note idea in Picc./Cl. 1. Is that part of the flute plane or not? Likewise, the 8th notes in the Glock./Fl. 2 plane also blend into the Picc./Cl. 1 plane, but then they separate again.
So, what separates planes of sound, anyway? In short, the musical dimensions in roughly this order: Rhythm, Pitch, Volume, Timbre. In long:
a. Things that are rhythmically the same are heard together unless you *really* work to separate them (e.g. super high/super low, super loud/super soft, etc.).
b. Things in the same register are usually heard together, unless rhythmically different.
c. The louder voice will stand out, but only if there is rhythm or pitch separation.
d. Different instruments will be heard differently only if separated by the other dimensions.
For an example of super crisp planes of sound, listen to the March from Holst's First Suite:
Holst uses two or three planes of sound through most of the piece, clearly separated by rhythm and register. The lyric middle section features two contrapuntal lines that are rhythmically similar but separate at points, but live in different registers and timbres (Clarinet vs. Euphonium and Bari Sax).
For your piece, think about how you can be clearer when you're layering ideas. That should solve most of the problems and let you get those pesky ffff marks out of the score. The section starting from 25 to 32 is a place where you nailed it. The rhythmic and pitch differentiation between the lines is great and lets the three voice counterpoint work nicely.
3. Too many dynamics happening at the same time: It's rarely effective to have more than two dynamics happening at once. No matter what you write, players tend to play at a level that balances (or sometimes overbalances) the sound around them. If a section or line is to be "to the fore", write that up a dynamic or two, but leave the rest of the ensemble at the same dynamic. You have to use rhythm and pitch to separate figures before you lean on dynamics to do it.
4. Always show the middle of the bar: You've got several syncopated passages with a quarter note on the + of 2. Trombone 1, m. 3, for example. This makes it really, really hard to read. A couple of examples where e=8th, q=Quarter Note, and _=Tie:
a. Trombone 1, measure 3: instead of | e e e q e e e |, do | e e e e_e e e e |
b. Flute 1, measure 13: instead of | e q q e e e |, do | e q e_e e e e |
In both cases, the tie will show the player where beat 3 is. It reads much cleaner and saves a lot of mistakes.
Keep up the good work on this! Refining and reworking are the toughest part of composing, but they are really what turns an idea into a real piece of music. You're on the right track.