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
as much as you can...