The KS01-BLV-2 is a SPST-NO switch with built in LED (Color is Yellow to match the Sinfonion). This project will be treating it as two different systems, the momentary press normally open switch and the LED indicator.
The switch itself will feed directly into the microcontroller, and the LED will be driven by the TLC59401 (we'll talk about this specific interface in a future project log). The TLC59401 will allow for each of the 14 button LEDs to be PWM driven, to allow for dimming of the LEDs and more advanced display options (while saving on pin counts)
The nominal LED current is 20mA with a 1.9V voltage drop. Powering it from 5V from the PWM signal of the TLC59401 will require dropping 3.1V at 20mA, or ~155 Ohms, and in reality it'll be will probably drive with a 220 Ohm 10% resistor.
Buttons will be read by feeding the 3.3V through the momentary press switch, while enabling the Teensy's native PULLDOWN resistor on the channel. Debouncing of the signal will occur on the microcontroller as well.
See the TLC5940 interfacing projects log for more details on actually driving these LEDs.