Apple Resources - AirPort Express

In April 2018 Apple announced the discontinuation of its
AirPort line, effectively leaving the consumer router market.
Apple continues to support the AirPort Express and AirPort
Extreme (all generations). Furthermore, there are rumors that
Apple is working on a new generation of routers.

AirPort Express  (1st gen) - Setup Guide

AirPort Express  (2nd gen) - Setup Guide

AirPort Extreme  (5th gen) - Setup Guide

Update the firmware on your AirPort base station

Recommended settings for Wi-Fi routers and access points  

The Checklist Podcast 89: Router Rundown (22+ min)

  Routers -- Most everybody has one at home.  But most of us
  don't know anything about our routers.  If the router gets
  hacked the bad guys can get everything!

  Problems/Bugs continue to be found in hardware, operating
  systems, applications software, networks, and technology.
  There is an ongoing battle between the good guys finding and
  fixing the problems and the bad guys1 finding and exploiting
  the problems. Your role is important in this ongoing drama!

  1Do bad guys include ISPs, Carriers, big tech and your own