do you mean that you want to build a device, based on teensy, which acts as a virtual serial device over USB, and speaks some subset of the OSC content spec (in other words, a device that behaves basically like monome controllers) ?
in that case, i’d say the trickiest bit will be the serial USB code. fortunately there is a PJRC demo for that, maybe you’ve already seen:
https://www.pjrc.com/teensy/usb_serial.html
then you will implement your content format on top of that. if you want your controller to behave like a monome device it should implement the serialosc format:
http://archive.monome.org/docs/tech:serial
, but maybe you have something else in mind.