Well, well, well, this is an interesting little post.
First of all (and let's just get this out of the way), it's Brandon Sanderson. His name's on the board, look up above the name of the thread and you'll see it there, "Brandon Sanderson." It's also on the book you read.
Next up there are many differences between Dan Brown's and Brandon Sanderson's books. I'll just get into one. Genre. Brandon writes FANTASY. Mr. Brown writes HISTORICAL FICTION. Dan Brown's books are supposed to be believable because he sets them to take place in our world. Brandon, makes up his own world, and thus, things don't have to follow the rules of our world. It's called magic.
Thirdly, it does mention in the book, that if a Mistborn does not burn away the metals (magically), before sleeping, they are indeed poisonous and can be very bad for you.
It also says in the book that not all metals are allomantic ones. What you spelled 'atrium,' (I shouldn't be talking, I'm pretty much the worst speller on the board
) should be called atium, and it is in fact atium, a metal created by Brandon, and not silver.
I hope this answers most of your questions Utopia, welcome to the boards.
EDIT: Oh, and I believe Warbreaker downloads are free from his website
www.brandonsanderson.com. People have been reading it, and giving him suggestions, before it goes to publishing, at least that's what I think. I haven't actually read warbreaker yet, but I think that's what is going on. I think he's on draft 6?