Open VPN client over relayd wifi bridge

I think what you propose isn't going to work when your openwrt router is running relay configuration and you also want openvpn client on same device. There was a similar post from another member on this forum a few weeks ago. Devices which want to use the vpn tunnel must be on a different subnet for success.

You can check your openvpn client router is functioning in normal router mode when ethernet wired to your main router. See my PDF for helpful advice.
Maximum openvpn speed using C50 v3 or v4 is 13 Mbps over ethernet btw.