Sounds like what you want is a smart/managed switch.. There is no reason to route this traffic over pfsense.. If you want your nas to talk to something else to copy its video too, then that something should be on same layer 2.
I would agree you prob don't want all your other network stuff on this same network. So you put your camera stuff on its on network/vlan ie layer 2. Now be it you want to talk to this stuff from another network or allow it to talk to other stuff via layer 3 then sure that would route through pfsense.
Having another nic in pfsense would allow for having multiple nics for your other networks so you don't have to put everything on a vlan sharing the same phy speed limitation of 1 nic.. But once you get switch that supports vlans pfsense could be used with just 1 nic, etc.
Isolation/separation of networks is yeah good security practice.. I sure don't trust all this iot stuff to be on the same network as all my other stuff. So yeah they all get put on their own vlan.. They can talk to each other.. I let them talk to the internet - but they don't talk to any of my other local networks. For example nest thermo and nest protect. They are on their own wifi segment. They have no access to anything else on my network. Once I get a cameras setup it would be the same way, my directv dvr is on its own segment, etc.