connect a 2nd router to the panoramic modem?
Yes it can be done. Just plug the Ethernet cable into the yellow WAN port on the router(s). Then configure the routers to use different subnets 192.168.*.1.
Replace the * with any number between 2-254 and it should configure it just like it's connecting to a cable modem.
As far as it being a good thing, I use a second router off of the panoramic wifi modem so that I can bypass Cox DNS servers and use my PiHole to trap any ads before they reach my devices. Highly recommend it.