Ppoe to dhcp gateway to subnet dhcp router to switch to ptmp

ppoe gateway which i want to tell mikrotik router the ip of new devices to add to mikrotik arp list

So i can manage firewall on the tik from an incoming gatewAy and incoming dhcp

I was thinking

Dhcp relay?
Maybe Vlan is my answer or

Some sort of subnet config where tik recevies dhcp from the gateway and then i can apply layer 7 and raw firewall on the mikrotik and then forward this out to

//A switch where the switch is being issued dhcp from the mikrotik
And the mikrotik is being issued dhcp from the gateway..

???