Before I share what I've learn and done, there is a caveat that was pointed out by another poster.
Most modern devices with wifi these days has drivers which looks at signal strength and figure out when to switch over to another saved wifi profile and varying thresholds. Some older devices has less intelligent methods to switch and could hold on to a wifi AP as long as there is even a little signal. The finally there are some devices that doesn't know which AP to use if both AP has the same name (SSID). Among these I discover are Nest devices. They cant connect correctly when more than 1 AP are around with the same name (I worked around that).
But for the most part you need at least 1 NAT router where you share your internet point to other devices. These days, NAT routers are combined with WIFI AP capability. My setup is just a NAT router without any WIFI (I turned it off). I then Have 3 additional WIFI routers to create 3 APs with the same name BUT different channel -- make sure the channel is different!
For example:
2.4G SSID : 2.4G_WIFI = AP1 chan1, AP2 chan2, AP3 chan3
5G SSID: 5G_WIFI = AP1 chan4, AP2 chan5, AP3 chan6
Each APX represent a uniq and supported channel band.
For example on AP1, AP2, and AP3, the 2.4G network must to configured exactly the same in every way except for then channel number. Same for the 5G network.
These AP are connected via ethernet cable to my router and are set up as Access points only. Make sure you buy devices that allows you to configure them as Access points. Most wifi routers has this capability. Be careful not to configure them as routers.
For my Nest device, the workaround requires your AP to support an advance feature to additional virtual access points. I created an access point using different names such as:
AP1_2.4
AP2_2.4
AP3_2.4
AP1_5
AP2_5
AP3_5
While I configure my phone, and tablet to use the common SSID such as 5G_WIFI, because the Nest cannot do this, I have to pick the best AP closes to each Nest device.
In my use I went with cable and access point because I got lucky in my setup where I can fish a cable inside my drywalls to where I need them to be.
You can also use wifi-repeaters if you cannot get a cable there; but you will lose half your bandwidth to support repeat mode. Half will serve your clients, the other half is used to communicate with the Access point it is task to forward to. This needs to be consider as you 'design' or architect your home wifi setup. If you're using a old and slower wifi router such as 54 mbits, that would mean less than 27 mbits shared between clients. This may not cut it if you hope to watch videos in that part of the house. If you need to use a repeater and get good speed, you may need to upgrade BOTH routers to AC, so you can get somewhere like 900 mbits/2 theoretical speed to support the speed you need.
If you're just checking email and webpages without videos, maybe you don't need a pair of AC access points for it.
My hardware setup:
pFsense firewall/router (Cisco E4200 backup)
Netgear Nighthawk AC1900 (with dd-wrt) central wifi (middle of my house); wired to my pfSense
Edimax AC1200 in Garage. wired to my pFsense. Gives coverage to my garage and front of my house.
Edimax AC1200 in basement, far side.