Wireless configuration

I really do not know what yo mean by configuration. Maybe this will help

Recommended settings for Wi-Fi routers and access points - Apple Support

You will need Routers capable of 802.11n or ac, and dual-band with both 2.4GHz and 5GHz will be vastly superior without being much more expensive. Routers that support only 802.11g or only 2.4GHz are not worth paying any money for today.

If you use Apple Routers, these can be combined to provide a single named network and allow seamless movement of portable computers with handoff from one to the next, if you desire. Some third-party Routers support this feature as well.

Exactly ONE of the Routers should dispense local IP Addresses using DHCP, and the rest should be set to "Bridge" mode (or have DHCP turned off -- the terminology varies but the effect is the same).

If all eight conductors are present in your Ethernet cabling, and the Routers are Gigabit Ethernet capable, you can transfer packets at Gigabit speeds. This is useful for local file transfers, but not necessary for Internet access, because the connection to the Internet is always slower than Gigabit speeds.

The Airport Express has only one "User" Ethernet port (and one "trunk" Ethernet port) so if you decide to install more than one Ethernet device at each of those locations, you will need to buy an Ethernet Switch to add on later. Ethernet is many times faster than most Wi-Fi, so it may be a concern in the future.

The Airport Extreme has support for 802.11ac and better radios and multi-stream support (faster if your MacBooks are new).

Both have been available as "Apple refurbished" units. "Apple refurbished" units are pristine and like new, and have the same warranties as new. They must pass the same acceptance tests to ship as new, but save you a few bucks. They may have been used for a demo or a show, or be customer returns that are perfectly good, but cannot now be sold as new due to commerce laws.