For a LAN-LAN-firewall realised with a Raspberry Pi you need a second LAN interface (via USB), only RasPi 3B+ an 4B provide Gbit-Ethernet (1000Mbit/s) and only a RasPi 4B is equipped with USB 3.0 for Gbit USB-LAN. The RasPi firewall will be the bottleneck in your network!
Yes I am serious! You thought I was joking? Have you seen Amazon EERO? It has all the above and more. Pi-hole replaces many paid services and hardware alternatives available in the market and am hoping see one day it does what EERO does.
Hope you did not get offended by my request.
So many people confuse router and access point. Very different and separate beast. A router can contain an access point but a router is not an access point. Gotta love the consumer crap out there that has basically confused the public. On a side note a Raspberry Pi could not handle routing any decent connection. Not only do you need a minimum of two ethernet ports, the single onboard port it does have can’t even handle the speed it’s rated for. On a side note you could technically route with a single port using vpn concept but it’s way above the skill set of most users. We’re also back to the under powered hardware which would seriously choke the network.