Good luck at the contest!
It would be useful to know the scale (1/16 I assume) and the manufacture of this kit. Is it resin or plastic?
Weathered helmets & canister help with realism to convey the idea they are metal. Its hard to tell from the pictures but the leather web gear & skin should have a slight shine, this is a easy correction as grease from your own skin can be brushed on for this effect. Your own forehead works well, brush & apply to the areas shine is needed.
Lead pencil can add a few chips to the metal gear, keep it restrained & random.
The skin tones & hues look great! Keep building & posting your work [So]Rice