1.Fork our TouchMIDI firmware.
2.Customize and build your own project on MPLAB X IDE.
(MPLAB X is IDE for PIC MCU. You can get information here.)
3.You can use much more terminals than PAD1-10.
If you want GPIO, you can use IN1-4, OUT1-4.
If you want to connect to I2C devices, you can use SCL/SDA.
If you want to use UART, you can use TX/RX(not only MIDI).
Detail of Each Terminals is here.
4.Write your original firmware to TouchMIDI by PICkit3.