1) LEDs: https://www.aliexpress.com/store/701799
2) Library: http://fastled.io/
3) Have fun ;)
On fastled.io, check the "community" link for tons of examples. This is a great time of year to find fun/cool projects as well.
I'd recommend a Teensy board over an arduino. It's many times faster, which is crucial for long strips and timing.
Paul (creator of Teensy) has some other really cool writeups as well, including building a giant TV out of the LED strips.