To be clear, there is nothing downstream of the Actiontek except for wireless connections, and that's currently limited to a single laptop that only sees occasional use. I kept the Actiontek as a standalone device so as to avoid any such IP address conflicts. I wouldn't even be using it were it not for the fact that I still have one STB in use on the upstairs bedroom TV. I intend to disable the wireless function and set up wireless on the pfSense router at some point. For now, I just want to get the basic internet features working.
In any case, I have found the problem and got it working. Apparently the "Block bogon networks" checkbox is checked by default and it was preventing the router from allowing internet access. I had gone through one of the tutorials yesterday and it jogged my memory when I was looking through the various configuration screens. I reset everything back to factory defaults and reran setup from the beginning, but this time I unchecked the "Block bogon networks" box. When I was done the yellow exclamation mark next to my network access icon disappeared and I was able to connect to the internet.