Another solution, although it might be a bit more complex and depending on parts pricier (even though an old PC works like a charm, I use an old Opteron 140 based PC for it), but you could try building a PFSense box and using it as your router, inside it you can configure the firewall to let in only connections you trust and also you can configure a router level antivirus.

Been using this system in my house with around 40 to 60 devices connected from all my family and haven't had any issues so far. You can also use VPNs at router level and a whole lot of other configs like packet sniffing if you're extra paranoid about security

For standalone AVs in Windows, Kaspersky is a good option, Bitdefender is meh sometimes, idk if it still exists, but the Comodo AV and Firewall were pretty good to keep PCs safe and avoid server intrusions (used this while working in a company to block their server from installing the programs that the company wanted and installed what I normally used)