Regarding the devices I like the Archer C7 V2 (EU) or the Netgear R7800 (after reading lots of threads here and flashing them).
For the full house network coverage there are a couple of interesting challenges.
Just one I want to point out to is the 5GHz requirement - maybe to sort it out. Yes, there is a huge advantage of 5GHz which is SPEED and better signal quality in wifi station crowded areas. Whereas I don't "know" what the latter is - I receive 25-30 at home, and with that number I don't encounter any problems.
With the 5GHz I have a big issue: I receive it in 10% of all rooms in a house that might be similar to what you describe.
This brings up:
- Band steering ("Bind" client to specific SSID vs "band steering")
You will be even more disappointed with the 5GHz / 2GHz roaming capabilities of your devices than with 2.4 GHz only - (5 GHz) Network is available in 10% of the house space only (Compared to 2.4 GHZ --> 90%)
Which is useless, in that area I could also use LAN cables
Which makes it really difficult to make 5 GHz available on all floors in all rooms. Not sure, but I would need about 4-5 devices (router + access points) (nice guide here https://openwrt.org/docs/guide-user/network/wifi/relay_configuration).
For me, 5GHz is really weird and practically not usable or I have very unusual walls in the house.
I will also start to look for a very cheap device (20-40 EUR) supporting 2.4GHz (maybe only if cheaper) to set up one Wifi extender. Update: Got a TP-LİNK WR1043ND v3 on ebay Kleinanzeigen for 24 EUR. Awesome cheap and neat.