I would not- doubling up on AV programs usually eats up system resources and causes very slow performance.
2. How do I completely delete the Norton product?
Get the Norton removal tool here:
3. Does anyone have any experience running Comodo? Good? Fair? Bad?
Sorry, never heard of this one. Sounds good, but you get what you pay for. I'd be suspicious there is a hole built into it to for reporting your browsing habits (marketing). If your computer is behind a router with a correctly configured firewall you don't need more than the windows firewall.
AVG Antivirus and Firewall combo runs very smoothly with no hang ups. I’ve been using it for over 18 months and it’s the best combo I’ve ever used. I’m even thinking of upgrading and adding the Spam control as well.