I'd still suggest making a system image backup.By using this setup,avast with comodo firewall,of course,would i not need a system image backup solution as i don't want to use such product.
and is this setup light on resources?
Comodo Firewall is incredibly light. Avast runs light for me with no noticeable slowdown but your experience may differ. I'd suggest running the setup for a few days and seeing if you're happy with the performance.