Sounds like this could be a fun project. I wouldn’t be able to participate personally, but here are a few thoughts.
You’d probably be best off with a mixture of levels for the materials, meaning a combination of high-level, medium-level and low level communications and documents. An example at the highest level would be an address to the nation by a political leader; an example at the lowest level would be a soldier’s diary. A mixture would be more interesting than just one type, and it would also get around the limitations of using just material from individual soldiers and sailors. There are potentially several problems with using just material from individual servicemen. First, their strongest asset (the on-the-spot detailed immediacy of their experience) is also their greatest weakness (the fact that it doesn’t convey the big picture). High-level communications have the reverse problem, so using both types solves both problems. Second, A&A units represent large forces (potentially as big as army groups or fleets, depending on the context), so tracking an individual person within those forces is problematic unless you basically work from the principle that “the person dies when his whole unit is destroyed.” Third: if the person dies, you have to either end the narrative thread connected to that person completely (in which case you may end up with fewer and fewer narratives as the war progresses) or assign a new serviceman to pick up the narrative thread when an original one dies.
I once read a book on tabletop wargaming which included a chapter that showed how much fun could be had with extras of the type you’re proposing. In this specific context, the author’s campaign-level game (which went on for months and which involved multiple play-by-mail players and himself as the central game controler) featured a newspaper that was technically based in one of the kingdoms in the fictional game universe (though in the interests of balance it was actually managed by the game controler, not by the player who was in charge of that kingdom). The weekly newspaper (sent to all the players) published a mixture of news, propaganda, lies, rumours, advertisements, and so forth, including unflattering allegations against the enemies of the kingdom where the paper was technically based. (For instance, one issue contained a story implying that the wife of the ruler of an enemy kingdom was a little too fond of the cavalry officers attached to the royal household.) One player became so outraged by this journalistic abuse that he invaded the kingdom where the paper was based, took control of the whole country and hanged the paper’s fictional editor. The game controler, who was the real “editor” of the paper, had to do some fast thinking because he couldn’t allow the paper to actually fall under the control of a specific player (which would have made it a true propaganda vehicle), so he used his powers as game controler to stage a nationwide riot in support of freedom of the press. The paper therefore went back to its original editorial policy, which was to be “equally unfair to everyone” as much as possible.