This reminds me of trying to play Half Life Alyx on an Oculus.

And a 100% reason to remember the name

Doesn’t need to be the case if you segment your network to protect against ARP.

Don’t have the Wi-Fi network “upstream” of the LAN. You want the connection between the LAN and Wi-Fi to be through the WAN so you get NAT protection.

The risk is the ISP Wi-Fi. As long as you’re using WPA with a good long random passkey, the risk is minimal. However, anyone who had access to your Wi-Fi could initiate an ARP spoof (essentially be a man-in-the-middle)

As an FYI: this set up is vulnerable to ARP spoofing. I personally wouldn’t use any ISP-owned routers other than for NAT.

That would do both, but I wouldn’t buy that personally. Make’s troubleshooting a connection problem more difficult, and also if the device fails there’s two things you have to replace instead of just one. I’d go with a separate cable modem and router.