You have two things to do.
- Translate input switches into MIDI note messages.
- Have extra switches that you translate into MIDI change voice commands.
Until you have worked out how this is going to happen then there is no need to worry about the software which is rather trivial.
As an example of how trivial it is see the code in this project:-
http://www.thebox.myzen.co.uk/Hardware/Pendulum.html