i've always thought it was much harder to play guitar than piano. i guess to me piano has always made sense because a majority of music theory is based on the keyboard's layout. C to C on white keys is the pattern for all major scales for example.

in terms of what to read or view first, i don't really remember a time NOT knowing piano so i can't really give you too many adult examples of good study materials. Alfred is who taught me piano back in the day and I know their children's series are very well laid out...i doubt you want to learn it like a kid. they probably have decent adult books however if you want to give them a shot: http://www.alfred.com/Bro...PianoKeyboard/Piano.aspx

When I got older and needed to focus more on technique, my teacher would assign pieces to me that has certain things in them. ie - when i was learning more advanced scales, she assigned pieces that had huge scalar sections, etc. i think you'll need some of the very basics (fingers, etc) to be successful and then once you get notation down, you can start picking up songs you want to know. i tell my students all the time that you need to learn the basics first but then pick something you're excited about because you're more likely to practice and ultimately retain the information you're trying to learn. works with instruments, too.