Well wouldn't the input frequency from the guitar be a sine wave?
Would I basically need to take the input and run that through an amplifier and then use an RC filter to keep the signal from 0v to 5v? Then I imagine I could use the frequency counter libraries or pulse count to log the frequency over a set period of time?
The reason I want to use LEDs is just to have practice with writing code and routing the signals to the different pins on the Arduino.