Network review
Network review
The layout looks promising. It should work if you set up separate IP addresses for each router on distinct LANs, ensuring no interference between them.
One PFSense unit with multiple network cards can manage separate networks independently. This setup lets you configure distinct LANs on the same router while keeping them isolated.
As long as the firewall or router lets you isolate the second subnet from the main network, you should be okay—no need to fully deploy pfSense.
You're facing an issue where you need to set up a double NAT for the second network, and because it requires using a LAN port on your first router, devices on network 2 can reach those on network 1. Adding a third router might be a solution if you're okay with managing configurations. Your diagram shows a basic setup with what seems like outdated tools.