For voltage regulation, you'll have to find the LM38T05 spec sheet. If you want one, just ask James or Kevin in the ECE lab for a 5V voltage regulator (give them the part ID to be sure).
The LEDs have a current limit, so what component should you use to limit the current?
The optoisolator spec sheets are here, here, and here. They should all work the same. I believe that the PS2501 (or maybe the MCT06) has a nice example circuit so you can see how the pull-down resistors should go (to effectively create pull-down voltage dividers).
Arduino Basics
There are also a set of experiments for working with the Arduino.