Roger has decided to build his own router as a project using an older computer. What would be the best operating system for it and how should he configure the LAN? Leo says that's a project that Leo has wanted to do for a while now. Steve Gibson has also talked about the DIY router project and uses PF Sense and the NetGate SG1100 with an ARM chip to run it. He likes it a lot and it's open source. It's the way to go. You could also use a Raspberry Pi.
As for segmenting the LAN, you may have to put extra ethernet connections, but it should be a simple thing through PFSense. But remember that any IoT devices will be a gateway into your network, so you'll have to pay extra attention in locking it down.