What ones should I get?

[Kuja]

DO NOT play the ff7 spin offs or watch the movie before playing ff7. They will provide more misdirection/confusion than anything.

That's not exactly true. I think if you do play FFVII: Crisis Core, then your safe. I honestly think it helps you understand the storyline of VII a bit more. I remember, during my first playthrough of VII, thinking, who the heck is Zack? And Crisis Core helped me understand who that character is, and what happened.

But definitely give VII a try, and get IX too. Those are both great games.