If you really want to slim down with avast resource usage you can disable all the shields accept the Standard Shield b/c it scans everything accessed anyway.
CFP and avast work well together and are a great combo. default settings, esp. for CFP should be fine
I have CFP 3.5 and Avast 4.8 Home and no problems for couple years now. I only run the Standard and Web Shields set to “HIGH” and do not use an email client at all. Yahoo webmail only.
Avast doesn’t recommend putting webshield on high because if you are downloading a big file that will slow the pc down because it will scan the downloaded file espeially when using a bittorrent app and downloading big files.