No, no. I, personally, would not use a software firewall along with the router's built in firewall, but that's because I'm fairly careful with my surfing habits - I don't think it's likely I'm going to get a trojan, for example.* If you want, you can run them both, but there's always a chance that they'd interfere with each other.

As for what you need in the main setup screen, you'd most likely have to ask Comcast. It may just work with Automatic Settings - DHCP. Mine does.

"it came back to me to limited or no availibility"

Um, I don't quite follow what you mean.

*this is not a challenge to you all