Buy neopixel strips here.
Buy power supplies here. This is the 4 Ampere one we used in class. It can comfortably power as many as 67 neopixels. This is the adapter we used to connect the power supply. (Barrel connector to alligator).
I don’t work for Adafruit, and I don’t make money off of them. I buy from them because they have good products and excellent documentation and libraries and tutorials.