Why would you buy a firewall? If you're already running Linux just use that or use the one in the WiFi router you probably already own. You don't need 2 APs, I don't know where you're getting this from. It's a home network. And why would you need an 8 port switch? You just need 2 ethernet ports on your Linux box to pass the connection through to the Wifi router.
How are you going to identify devices? MAC? DHCP reservations? Static IPs?
Yes.
That's not a trivial project.
I do this stuff all the time, it's not rocket surgery.
Because I value uptime. I don't want my garbage PC that runs PiHole to crash and totally take down the network.
I have many hardwired devices, they may not.
I need two APs as I live in an older house and I get crappy reception in my basement. I also want a guest and IoT network so I chose to use VLANs to segregate, which requires switching and APs that can do that.
Yes, if you do this all the time (I do too) it's not that hard. But it's certainly not a beginner project.
How are you going to identify devices? MAC? DHCP reservations? Static IPs?
Yes.
That's not a trivial project.
I do this stuff all the time, it's not rocket surgery.