If you’ve an OpenWRT compatible router why are you thinking about pfsense? There isn’t much to gain there, your OpenWRT will do NAT and also has a firewall.
I like this device since 3ports would allow me to create a physically separate DMZ
OpenWRT can do this as well. What are your plans with the DMZ tho?
Be careful with the use of the acronym DMZ as in the context of typical routers and ISPs it has a different meaning of what you’re implying here. DMZ usually is used in the context for a single host that is “outside” the ISP router’s firewall and all requests coming into the ISP router will be forward to that device.
With my current diagram, it seems like it is not possible for the NAS to receive updates from the internet.
You NAS will never “receive updates” it will ask for updates. Maybe add a firewall rule that allows traffic from the NAS to the internet but not the other way around (this is usually the default state of any router, it will allow local devices to go to the internet but not incoming connections to those devices).
My TrueNas has 2x2.5Gb ports. Can i connect each NIC to a different network? Would this have any benefit?
You can, but is it really worth it? If someone hacks the device they’ll access the rest of the network. Same applies to your computers and cames consoles, they can be used to jump to the other side and vice versa.
Frankly I don’t see the usefulness of your setup as you’ll end up with weak points somewhere. Just get a single OpenWRT router and throw everything into the same network. Apply firewall restrictions as needed.