I use 12v, but the principle is exactly the same. Just make sure it is the right voltage for you.
Don't use USB for just power. You can get 5v and 12v from a spare molex power connector in your PC.
red is 5v, yellow is 12v, and the two black ones are the grounds (for the active/coloured lead closest to them).
get a new molex connector, or a molex power splitter cable and chop that up. The rest of the wiring is very similar to what you'd do for buttons, so daisy chain the grounds. You can also daisy chain the active.
LEDs are very low power, so you should be pretty right for a few lit buttons, unless you want to make a Christmas tree out of your cab.