Yes, you are correct, obviously I only need one router, what I was trying to say is that I want to have three APs in total, one also being the router. The router is located in the technical room on the first floor, then I have one AP at the 3rd floor, and one AP on the loft of the separate garage, to cover computer and stuff in the garage and outside, for cars, EV charger and mobile phones in the garden etc. The house is about 3300 sq ft., first floor has concrete walls, but everything else is wood and plaster boards. I think the current setup is fine when it comes to number of APs, the real issue is stability. Dropping out is very annoying.
The reason I mentioned I need the mesh net to also include a router is that the mesh net cannot just be APs for the ISP-router, as I also have a second network connected to that ISP-router, to have two separate LANs (separate apartment).
The mesh net I have today is already wired, and I plan to continue with that. Only issue I have seen with that is that with Asus they have to be connected directly to the main AP/node, it does not work when they go through a switch.
I prefer wired for anything I can, so anything related to TVs, most of the Sonos speakers, computers, smarthome gateway, heating systems, printer, etc. is on wired connections. Wi-fi is for smoke detectors, solar panel inverter, EV chargers, cars, cell phones, ipads, laptops, 3-4 Sonos speakers (I also have a Sonos boost), etc., but it does add up to a number of clients, and some of them are probably very low bandwidth, maybe affecting the quality of the network for other clients as well.
I have tried with separate APs with different SSIDs before, but it was a definite improvement with AiMesh and the same SSID all over (although one for 2.4 Ghz and one for 5 Ghz).
Budget wise I am of course hoping to pay as little as possible for the desired functionality, but I rather pay a little bit more to get a decent product.
I do not think I have any Wi-Fi 6 devices at the moment, so not important, but I appreciate something future proof.