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)
ETA: the ARP table in networking is a cache of which IP is associated with which MAC Address. By “poisoning” or “spoofing” this table in the router and/or clients, a bad actor can see all unencrypted traffic.
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.