Not sure i this helps you…
To enable openvpn autostart, ensure you have service enabled /etc/init.d/openvpn enable. Check UCI config /etc/config/openvpn if you have option enabled '1' for that openvpn-client setup. That should bring all enabled openvpn instances after bootup. In case you do not want autostart, you can use /etc/rc.local and you can add startup command there.
Some inspiration: [GUIDE] OpenVPN Reconnect-Script | Daily restart with location change! | Server Roulette | Client to stay allways-on | Luci vpn nano ssh linux
With routing,you can create dedicated CCD file for client or you have to alter the server config and add push route there.