I’ve got a mix of devices for WiFi.
At the front of the house is a 4th gen Time Capsule (2011 vintage).
At the back of the house is a 3rd or (4th gen??) AirPort Extreme (2009 vintage??)
One wasn’t enough to get across the whole house so the second one is cabled in to provide that extra coverage.
I’ve also got a couple of airport expresses that I used to use as wireless bridges when I was in a rental that are used in the middle somewhere too. Similar to @purana one is providing an ethernet port to a stereo in the kitchen unless I get a cable run there one day and one is being used to provide a USB port to a printer (which makes it a network printer!) until that dies and I get a new printer.
Setting up Apple devices is dead simple, just tell it to add to the network and away it goes. From what I gather all this does it copy in the SSID and password to the newly added device. The idea being that each device connecting only needs to know one SSID and password and can connect to whichever WAP it is getting the strongest signal from… theoretically this can happen with multiple different providers hardware, I think the only thing that having all Apple does it manage the channels a little better to ensure they aren’t clashing with each other?? Although the big question is are they talking to each other to do this??? Or are they each automatically trying to skip around as needed.
I keep considering getting one higher powered device (probably ubiquity) and putting it into the roof space in the middle of the house (using power over ethernet) and having a single WAP… or maybe still one at either end. For the moment everything is working so I haven’t felt the need, that and none of my devices support wireless AC yet so there is no real benefit.