That is great effort. However, I cringe seeing how you apply the bondo. I'm not sure what you used but there are too much lumps. I did something similar when I first applied bondo on the scout helmet. It took me hours to sand off the extras. You may have used the wrong applicator.
On the helmet areas that bend, I suggest that you don't fold them (see the ODST chest pieces that prepped. Less bend less bondo.) When you apply the bondo, use a wide hard plastic piece. Don't use metal because it can't bend around round edges. I used the clear toy packages because it was hard enough and yet bendable. Put some bondo on the plastic applicator and apply the bondo like applying peanut butter on a bread. You get smoother bondo, which translate to less sanding.
To sand, you may want to invest on an electronic sander. It takes minutes instead of hours.
