So far I've been looking at various things. I've started with the following 3 steps/questions.

1) What do I actually want the device to do?

2) How should the user interface be set up?

3) Spec parts

As usual, answers to these questions just brings more questions.

1) Should the device generate a single waveform, or multiple waveforms? This changes the type of DAC that I will need to create.

2) There's only 28kB of space on the trinket. A complex UI using something like an OLED screen will most likely not fit on top of the waveform code. Let's go with buttons, people like lots of buttons, right?? Especially with no visual feedback...

3) It ends up that in all actuality I found myself trying to spec the parts to fit my interface most of all. That's when I realized things might not be as easy as I hoped as one crucial part eludes me.

In the mean time I have parts on order for fleshing out a prototype. Once I have a reasonable prototype worked out I can get back to worrying about the end product. Current system model is as follows, nothing too complex.