Can this router be configured as a switch with the 1st port included? I need the poe in port to be included on the switch. Thanks.

only ports 2 to 5 can be switched

Create a bridge with port 1 and port 2 as members. I have several RB750UPs operating in this mode

Once bridged do I need to remove the dhcp server and firewall rules programmed in the router?

How should I configure for this setup. Main router -> Rocket AP WDS mode -> Nanostation In Station WDS to port 2 on the RB750up. Port 1 on the RB750UP is a POE out from injector. LAN side of injector is WAN on customer Router. DHCP server is on the Main router. Another Nanostation Access point is also plugged into the rb750up (port 3).

I've bridged the ether 1 and 2. And don't get anything

If you don't need it, you can remove the DHCP server.

The firewall filter rules in the default config only protect the router so they can stay. You probably need to remove the default firewall NAT rule