Every sub-system is working now that the Teensy is up and running. I developed some simple unit tests to help debug the board and soldering.
The test code can be found here and used to get your own communicator debugged: https://cdn.hackaday.io/files/19700842844800/Unit Tests.zip
The final step: Get the RF module up and running. First, I will verify the connections with some existing breadboard code. After that, the more major task will be to merge both transmitter and receiver code into the same file.