My final project will require microphones, pumps, and maybe LEDs, so I'm thinking about making separate daughter boards for the functions. It's all being housed together, so the serial bus would make sense. Rob explained to me how I can deal with voltage regulation (the mics run at 3.3v, the pumps at 5v), between boards, by putting regulators on the modules. I started drafting up the plans in Eagle.
At this point, I got pepper-sprayed in the train station, and long story short ended up leaving town for the rest of the week. When I came back, I was in a huge time crunch, and trying to work on both composites and my final project. So I didn't finish networking, and then realized that it would be easier to not have multiple processors involved - just separate modules, connected with wires and DuPont connectors or ribbon cable headers - so that's what I did for the final. See the Final page for the results. I'm hoping to have time during J-Term to work on networking and follow through on some of my weekly projects.