It will be better to use rpi as router and buy normal wifi router. Also i dont recommend rpi because usb-eth adapter will be bottleneck here. Instead i recommend something like nano pi r4s, nano pi r5s, orange pi r1 plus because they have dual gigabit ports (one for wan, one for lan).
I have a pi4( with archlinux arm) which serves as an AP, but I couldn’t get a few things to work:
Throughput is terrible, I can’t make it better
Can’t use the 2,4 and 5 ghz bands at the same time (hardware limitation as I read)
Can’t host multiple SSIDs on the same radio.
Openwrt v21.0.3 on rpi4 (I used squashfs) as an 5GHz access point on channel 44, 80MHz wide, seems solid to me. WAN on rpi4 NIC, no VPN. I tortured this configuration for days and it stayed up before switching to another experiment. The range isn’t very good, but that isn’t surprising as there’s no big antennas.