PPPoE and a static subnet - how do I use the rest of the subnet?

[ChrisC]

Hello all,
I am running OPNsense 21.7.5 on a Dell server with 4 NICs.
At the moment 1 port is configured for WAN access, which is configured with PPPoE to a fibre line that requires a VLAN tag.
Another port is connected to my internal LAN using internal IP addresses. NAT is working and everything works fine when accessing the internet from the LAN.

I have been given a /29 to use for my internet-facing stuff, and I want to run all this off a switch plugged into another NIC on the server.
My PPPoE connection is set to get an IP address via PPPoE, (which it does - the first IP from my /29 range).
How do I use the rest via a third NIC that I will plug into a different switch as a DMZ?
I have tried creating a bridge interface using the WAN port and this 3rd NIC, but nothing on that 3rd port is receiving any packets. Also, I can't ping the WAN IP (default gateway) from another computer connected to the switch on the 3rd NIC that also has a static IP in the same public range.

Should I be using a bridge as I have tried (and somehow my config is wrong), or should I be doing something else?

With other ISPs I have used in the past, the WAN port has a different IP/range to the local subnet (which makes more sense when using separate interfaces for WAN and DMZ).

Thanks!

Chris