There are about 3 things that I think you need to be able to do here
- Read the on or off state of a button
- Be able to send a message through the serial port (or instruct the fluxamasynth to do something)
- Understand what midi instrument you are trying to use as a voice for the midi stream.
Can you do the above? If you you have all the elements you need to carry out this project.
What libraries do you think that you need and why?