Step 2: Install/setup controller
Setup was easy. I plugged it into the wall outlet, plugged the serial connector to my PC, and that's it.
You need to download and install SDM SmartHome Device Manager. Now, once you've installed this, you can start sending commands to the PLC (PowerLinc Controller).
Since I had a MacBook in another room, I installed SDM Socket Server, which is freeware for Windows. This let me connect over TCP/IP from upstairs and send messages downstairs. Note: you need to edit a registry setting to make this software work with the Serial (COM1) port. HKEY_USERS\.DEFAULT\Software\Smarthome\SmarthomeDeviceManager
The port needed to be changed from USB4 to COM1.
Here are some various programs you might also find useful.