if i am using my pihole as dhcp server. should i set my router with ddwrt to DHCP server or DHCP forwarder under DHCP?
Forwarder, you can't have 2 DHCP servers on the same network segment without some involved work. One has to be the master and the second as a forwarding node to the master. If you want all the leases to show in one location, then forward the router to the Pi-hole.