Hey Zach,
I've been playing the piano (and keyboards) for 17 years now and I would really recommend taking at least a few lessons. Learning to play the piano is not that hard and you can do most of it on your own. However, there are a few simple techniques that you
need to learn early on, to ensure that you develop the right habits for moving your hands across the keyboard. If you don't learn those techniques, you will eventually reach a glass ceiling in the complexity of what you can play. At that point, it will be very, very hard to change your underlying technique.
As for finding sheet music, try
Sheet Music Plus. They seem to have almost everything.