Unfolding that model would probably drive you completely crazy.
Halo 4 armor has so insanely complex geometry that it doesn't really lend itself to a 100% pepakura solution anyway - these pieces are built from hundreds of thousands of polygons.
Although... you could get some pretty good results using Cereal Killer's methods, using a less detailed pep model as a start. But it's in my opinion a better fit for foam with all the layered detail; or some kind of hybrid solution where you use a lot of thin craft foam and other scrap items to build up detail, instead of trying to pep everything.
And of course you should simplfy, simplify, simplify
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as much as you can...