Subnet mask as possible helpful security measure
Separating the local network with subnet mask could be a helpful solution too using just a single router. This keeps the local machines unaccessible from the internet accessible Freedombox home server, should it get cracked into.
I.e., … using a subnet mask of 255.255.255.192, a local network of 192.168.123.0 becomes four networks: 192.168.123.0, 192.168.123.64, 192.168.123.128, 192.168.123.192.
These four networks would have as valid host addresses: 192.168.123.1-62, 192.168.123.65-126, 192.168.123.129-190, 192.168.123.193-254.
The binary host addresses with all ones or all zeros are invalid, so you cannot use addresses with the last octet of 0, 63, 64, 127, 128, 191, 192, or 255.