Now that the matrix itself is complete, it's time to connect what you've done to the Teensy. You'll be needing the number of pins equal to your number of columns + your number of rows. There are some pins on the Teensy that are special, like D6 (the LED on the chip), or some of the UART, SPI, I2C, or PWM channels, but only avoid those if you're planning something in addition to a keyboard. If you're unsure about wanting to add something later, you should have enough pins in total to avoid a couple.
Now that the matrix itself is complete, it's time to connect what you've done to the Teensy. You'll be needing the number of pins equal to your number of columns + your number of rows. There are some pins on the Teensy that are special, like D6 (the LED on the chip), or some of the UART, SPI, I2C, or PWM channels, but only avoid those if you're planning something in addition to a keyboard. If you're unsure about wanting to add something later, you should have enough pins in total to avoid a couple.