Sounds like it's really kicking!
Dumb question (from one not familiar the intricacies of the US marching band scene): is this intended to be played with some of the musicians on the move? Eg: sports arena of some description; mallets at the side; all other players doing choreography of one sort or another?
I'm assuming that the midifile is for demo purposes in terms of getting the whole production to the next stage, so final instrumental scoring decisions might not have been made yet. (I looked at the midifile in Sibelius.)
It's just that some of the brass ranges might be ambitious if the player isn't parked in a comfortable position behind a music stand. Every big band has a trumpeter who can play D's above the stave. (OK, every
college and upwards big band...) The same player might cack and sprawk playing the same music on the march in the middle of a pyro show. ("Realm of the Dragons" – ?? – I'm seeing flashpots – I'm hearing split notes.) Then again, if this were a
really big production, the TV feeds would be pre-records – you'd make sure you got enough foldback to enough players one way or another to keep in sync – problem solved.
The french horn/s – which came up as horn in Bb in Sibelius (??!!) – look/s unrealistically stratospheric. Nothing that can't be sorted out.
The other thing that came to mind: when the two minutes were up, I'd heard a lot of A minor. Nothing wrong with that
per se, but at this early stage I'd be looking at the possibility of introducing more variety with regard to key-centres. (You might be able to do some easy experiments. Save the original. In a copy, drag and drop some whole sections randomly, or even just use the pitch wheel if your playback setup allows. If it sounds like it might be worth following up ... etc, etc)
I found myself wishing that bar 56 was in a different key. For instance, just jump straight into F#m. (Hey – modulation's for sissies!

Or: modulate 'properly' out of the F#m section back to Am and the finish.) But ... bar 56 is probably too late in a 70-bar piece to go wandering for the first time. *scratches head in 'Colombo' manner*
All that said, it sounds like it could be a winner. Interested to see how it turns out.
cheers – jada