Tethering with WiFi and Ethernet on the same LAN

Hello everybody,
new user, I want to use OpenWRT on a Raspberry Pi 2B as a tethering router.
I already configured the system with WiFi on one side and usb connection to my Android smartphone sharing connection trough usb. It works great and I have a WiFi network 192.168.1.X routed to internet by the use of the Smartphone 4G data connection.
Now I would like that the Ethernet connection of the Raspberry joins this network so that:
1: any device connected to the Raspberry Ethernet port (directly or with a switch) can also connect the internet
2: Ethernet and WiFi devices can connect mutually over the "local network" (ie. a WiFi PC and an Ethernet printer or an Ethernet file server)
3: if possible have the same local network 192.168.1.X both for WiFi and Ethernet.

I think this is a common configuration, but I do not understand how to achieve this nor find any tutorial to... Anyone to help ?

up - please

if the ethernet port is assigned to the wan firewall zone, move it to lan, should be enough.

you want it green, not red