I have configured my Dragino LPS8 so it connects to my wifi and talk to TTN. I can also reach its GUI on port 8000 of its IP in my home network.
Is it therefore safe to switch off its “WiFi Access Point” (used for the initial connection), or can it still be required for something?
Just check there is no firewall on the WiFi client connection. If there isn’t you can switch the AP off. I usually connect the gateway with wired Ethernet but certainly switch the AP off.