You know, if you're going to include voice-chat in live multiplayer such as an FPS, wouldn't it be awesome if you treated your voice as if it were actually coming out of your character's mouth?
For the love of Gods, never pad a manual to 100 pages under the pretense that it's making the manual more useful. I realize that writing the manual's a mostly thankless job as in general no one but an attentive PC gamer will touch the manual in their lifetime, but that's no reason to cater specifically to that minority. (i.e. don't write the game manual like a technical manual, write it like a children's book) Outside of that, if you're needing to pad the manual because the game's just that complicated then you're doing something wrong in the design stage.
I'm already planning on having the Exhaustion Timer, Hunger Bar, and Thirst Bar disappear if they're currently irrelevant. Right now I see no reason why any HUD element shouldn't disappear when it's irrelevant.