I'm having a hard time visualizing how I could use only one interface. How would the rest of the devices connects? Or are you suggesting using as a wifi only router?

It's the "router on a stick" method. You use a VLAN-capable switch, and connect the upstream connection (cable modem, ONT, etc) to a port on one VLAN, while the rest of your network is on another VLAN.

I made a (bit complex) diagram. https://louwrentius.com/my-home-network-setup-based-on-manag...

> 1. It can handle up to 650 Mbit if you use firewalling with iptables

Is that at 1.5 GHz?

I was surprised by how powerful Pi 4s are. At 2 GHz they'll do cake at gig.

Correct, I don't know how faster Pis would perform.

I’m not too versed here, does using this project to make the RPi4 handle DNS make it a router? I’d rather not sacrifice nearly half of my gigabit bandwidth…

No, it would if it is in-line with your internet connection, thus forwaring ip-traffic.