Route Wireguard Over Ethernet To Device

Hello there,

I'm trying to accomplish the following:

I have an old Raspberry Pi B+ which is running OpenWRT.
It is connected via Wifi to my home network (192.168.178.1).
I have successfully (I think) connected OpenWRT to a Wireguard server.

Now I want to connect a device via Ethernet to OpenWRT so it gains Internet access but is running through the VPN. Ideally I'd like to be able to connect to the device from my home network as well.

Thank you very much in advance!

It would be best to illustrate the desired topology including the hosts involved in routing and the subnets for each network segment.