I'm not familiar with synthesizer-making so I can't help with your goal project, but as an example of a much simpler (no math?) version of "user picks a sequence of sounds, program plays sounds in order" you might want to check out the 'cylon' deck in the examples folder that comes with downloadable Decker (If you haven't already). It's not at all a singing synth. It only plays pre-prepared sounds... but the code is fairly simple, and the sounds files can be replaced with other things. It might be a starting point for a smaller jam project that can lead into your bigger goals.