Openwrt as switch and wlan router

Installing and Using OpenWrt
1

I have a Raspberry Pi 3b with a wlan stick and usb to ethernet adapter.
My goal is to connect the existing internet to the raspberry ethernet port. Then I want to connect a device to the usb-ethernet, which gets the ip address from the already existing network.
Then OpenWrt should make a wlan with dhcp server.
A cool addon would be if the wifi is an openvpn client.

I have already installed the drivers for the connected devices.

Thanks for any help in advance

2

See:

https://openwrt.org/docs/guide-user/network/wifi/wifiextenders/bridgedap#:~:text=Bridged%20AP%20configuration%20will%20use,device%20in%20Access%20Point%20mode.

https://openwrt.org/docs/guide-user/network/wifi/guestwifi/guestwifi_dumbap

You can setup a vpn client the guest wifi will use the vpn