If you have fibeTV then you need to keep the DHCP fonctionnal for the decoders. otherwise, its ok to disable.
looks like the wiring is OK SAGEMCOM --> D-LINK --->SWITCH
you need to setup the WAN side of the d-link in PPPoE and use your b1 code + password in the fields.
on Bell's network, you can use up to 3 times your b1 code at the same time.
that will give your dlink a public IP address and work as it was the frontline worker