My question is, Can OpenWRT put 2.4GHz traffic on specific vlans?
I've read some older forums that seem to point to OpenWRT not able to route WiFi traffic to VLANS. Without that functionality I won't be able to do what I'm intending to configure.
Yes, you bridge the SSID with the Ethernet interface that carries the VLAN you desire. Multiple SSIDs can be used (on wireless hardware that support them) to, for example, have a 2.4 GHz IoT SSID, another for guests, and a third for "trusted clients", all on their own VLANs.
If I understand that, I have to dedicate one Ethernet interface to VLAN 2 traffic from the 2.4 network? So I can't plug anything into it that I don't want to be on VLAN 2?
Once you get to devices that aren’t both VLAN-aware and trusted, you need to be down to a single subnet per physical net. Trunking multiple VLANs over a single Ethernet cable to a managed switch is common practice when wired devices are involved.
You don't need a physical port for your vlans.
Simply create a new wireless network on your 2.4 wifi device and add it to a newly created vlan without physical port.
The setup is really straight forward...
You don't put your ap interfaces directly to a vlan, instead you create a bridge to which your wifi and your desired vlan is attached.
For the networks without a real vlan, create also a bridged interface with attached wifi ap, assign ip and create a firewall zone for each.
If you are struggling with this setup, i believe you won't be able to setup the other desired services like vpn and captive portal.