I use one r7800 as my router and I use two r7800’s as APs. They work great and get up to mid 500 mbps (approaching the theoretical max for wifi 5) with a 2x2 80Mhz client in the same room.
I have all IoT on 2.4ghz and all user devices on 5ghz (different SSID for each band). I don’t have VLAN tagging (ehh, probably overkill) but if you are worried about your IoT devices you could easily separate them with a VLAN tagged to each SSID.
Feel free to try my build if you want to test how your r7800 works (NSS hardware offloaded so it can support your full gig line rate):