Wikipedia has acomparison chart of most Anti-virus software. You can decide how much protection your need and pay for. Please check out Anti-Virus sub

https://en.m.wikipedia.org/wiki/Comparison_of_antivirus_software

An interesting article https://www.lifewire.com/how-many-devices-can-share-a-wifi-network-818298

The Spectrum supplied free modem works fine with your own router.

I know each region of the world uses different channels. I use a free open source code app Wi-Fi Analyzer to help me see the traffic on a band.