Here is the circuit I used. Pin 6 goes to the data channel of the neopixels, and they get power directly from the external power supply and are connected to common ground. The external power supply also powers the arduino via VIN, and the arduino is connected to common ground. The two pots are connected to common ground and get power from the Arduino's 5V. Their outputs go into Analog in A2 and A3. The electret microphone gets power from the arduino 5V as well and that is also connected to AREF. Its output goes into A1 if the toggle switch allows the connection.

The line input has the same connections as the microphone but is switched via the toggle switch. It also is wired in parallel to another headphone jack that is used as a THRU jack. It doesn't matter which is used as input and which is used as output; both will function even when the device is off as a THRU jack.