I have a fairly large SteelBook collection. I definitely recommend putting them in protective plastic sleeves. I buy mine from Bags Unlimited. SteelBooks are very prone to scratches and dings if you put them on a shelf with no protection. Every time you pull one out (or a title next to it), the...
Rust, seriously? In what conditions do you live and store your movie collection that SteelBooks would rust?
As for the card, I typically fold it at put it inside the case.