Currently have five Deco X55 units, four of which are using ethernet backhaul, and one that is wireless backhaul (out in the garage where I didn't think to run a cable when we built the house!).

I would like to switch the Deco to Access Point mode and use a Firewalla Gold for DHCP and other network features.

The only issue that I am unsure about is the effect this will have on the guest wifi network.

In theory, the Decos will tag the guest wifi to whatever vlan ID I tell it to, so it should work. The problem is, they are connected via unmanaged switches that will not care about the vlan id. However, the "main" Deco would be directly attached to the Firewalla. So I am hoping everything would work properly -- meaning that the guest wifi would remain on its own vlan, isolated from the rest of the network, which is basically untagged.

Does anyone have any suggestions or experience or caveats for me with such a configuration? Is this even possible?