They are designed to mesh wirelessly using the 6 GHz band, most people don't need to hardwire them. You would typically only hardwire them if you see poor performance due to your home's layout or construction.
If you're going to hardwire any of your Wifi points, it's strongly recommended that you hardwire all of them. If you don't, you'll create a disjointed setup much more likely to cause problems that are very hard to diagnose. It doesn't matter whether you use the WAN or LAN port on your secondary points to hardwire them.
It should look like this:
Modem -> Primary Wifi point -> Switch -> Wifi Point -> Switch -> Wired devices
-> Wifi Point -> Switch -> Wired devices
You can also do this:
Modem -> Primary Wifi point -> Switch -> Switch -> Wifi Point
-> Wired devices
-> Switch -> Wifi Point
-> Wired devices
For switches, we recommend using an unmanaged switch or configuring a managed switch to disable Spanning Tree Protocol (STP) and forward Bridge Protocol Data Units (BPDUs) when STP is disabled. This will avoid technical issues with some managed switches relating to routing and network loops.
