I did a great deal of research to get to my current set up.
I have a 2300ft one level Frank Lloyd Wright like design with block walls that Wi-Fi doesn't like going through.
My office is at one far end and have strong Wi-Fi in the far back bedroom but this is what I had to do:
Main router connected to modem (use Cox) in office is:
TP-Link AC5400 Wireless Wi-Fi Tri-Band Gigabit Router (Archer C5400)
In walk in huge closet before the bedroom but behind a block wall I need this extender:
Amped Wireless ATHENA-EX, High Power AC2600 Wi-Fi Range Extender with MU-MIMO (RE2600M)
While may not be critical I also have in bedroom:
TP-Link AC1900 Wireless Wi-Fi Router - Long Range, High Powered, Dual Band, Gigabit (Archer C9)
In addition in my living room which is next to the office, I need an Ethernet connection for TiVO which I have
TP-Link AC1200 Wi-Fi Range Extender w/ Gigabit Ethernet Port, Small Footprint w/ Intelligent Signal LED Ring, (RE350)
If you have just normal walls and two stories you might get by just with the first AC5400.