Eh, it depends on what you value. Personally I don't care for steelbooks as I tend to like my game collection looking more uniform, but I like artbooks a lot so it was an easy choice for me.
No the story is unrelated, totally different universe. It does share some common themes and story elements (like Final Fantasy with crystals and chocobos), but they're not directly related otherwise. Gameplay-wise it's a sequel, as it builds off the previous combat system and the fact that it's...