Network Advice

Good Evening Level 1’ers.
Need a little advice I have had Comcast for years, I am running it with a DDWRT router. It was fine. I got lucky and I now have Fiber installed. So I have the DDWRT plugged directly in to the router that came with the fiber. Everything is working fine. Now for the question, I am trying to decide how I want to set this up.
What I am thinking is have my few open ports sit on the fiber router and keep all of the other network traffic sit behind the WRT router so that I have a true DMZ.
As a side not due to somethings outside of my control I have to keep the comcast connection so I am thinking of just doing an auto fail over. Is that what you think is best with having the 2 connections? Just looking for advice.

Thank you,

As a side note I am also thinking of maybe using a PFSense box to do the failover.