I’m not sure I understand your concern. If I read the diagram correctly, then you’re asking about configuration of lower-most device (controller) which doesn’t know anything about VLANs. So the configuration of controller will only run DHCP client and will receive IP configuration from DHCP server which is already running on centre router, serving eth5.vlan123 L2 subnet (untagged member of which should become ether1).
If you’re asking about needed (additional) config of centre router, then post current configuration of that router and we’ll help you adjust the config (if it’s a mikrotik device).
If my understanding of current state and desired config is off, then please describe things into more detail.