Best method to replace entire network (3 base-stations)?

How do your two client base stations connect to their router? You can determine that with AirPort Utility: if the lines connecting the two below are dashed (broken), then they connect to your main Extreme wirelessly. If they are solid (unbroken), then they are wired. From what you describe I believe you created a "wirelessly extended" network and you'll see dashed lines in AirPort Utility. Wired is preferable, but if they are "wirelessly extending" the first one's network, and that installation has resulted in acceptable network performance, the new Extremes can connect the same way and your network will function the same way.

Using the same network name for each Extreme is advantageous. Specifying different network names will unnecessarily complicate connecting from mobile devices, and could explain the reason some devices cannot connect on occasion.

I can think of no compelling reason to specify static IP addresses, but you can do that if you prefer to do so. It just requires an additional configuration step.

For simplicity, specify DNS addresses in the router, not the client Extremes, unless you have reason to use different DNS addresses for them (and again I can think of no reason to do that).

I avoided that question because I didn't think you'd like the answer 😝 but any time I change a main router I expect to reconfigure the entire network. Choose a weekend or other time when you are least likely to disrupt your office, then replace the main Extreme with the new one. Configuring it with AirPort Utility won't take long but until that task is finished you will not have any Internet connection, so if that's important to you decide what you're going to do about it beforehand. After it's configured confirm all the wireless clients within its wireless range can connect and work as expected: Macs, PCs, wireless printers, everything. Same for any wired clients, if there are any (VoIP phones, for example). For wireless devices expect the need for them to provide your wireless network's password again, even though you may have configured the exact same one.

Then, replace one Extreme, and repeat the above. Apple's AirPort Utility will offer to configure it automatically. It's OK to let it do that, but if you subsequently want to specify static IP addresses (for example) go back and edit those individual parameters.

If your experience is anything like mine you are certain to make an error or two in their configuration, so have a toothpick or similar tool so that you can "hard reset" any recalcitrant Extreme. Don't press too hard.

Maybe it has to do with cinderblock walls in the facility, I don't know.

Oh yes. You only have to endure the inconvenience of installing an Ethernet backbone once, but it's well worth the effort.

John may have some additional tips for you. I will offer a different idea, which I am not necessarily saying will be better.....but it will be different.

That would be to put Apple's "Replace an existing device" setup option to the test.

If this works correctly, this will transfer all of the current settings on each of the existing Airports to each of the new AirPorts.

You would do this one AirPort at a time. Here is the way that this would work:

On your "main" base station, connect an Ethernet cable from one of the LAN <--> ports on the "old" AirPort to the WAN "O" port on a "new" AirPort.

Click the WiFi icon at the top of the Mac's screen and look for a listing of New AirPort Base Station

Click on AirPort Extreme

That will open up a basic setup screen that will suggest a standard setup

Click on the Other Options button

Select the option in Apple's setup "wizard" to Replace an existing device

Click Next and follow the prompts

This will transfer all of the settings on the existing "main" AirPort base to the new AirPort Extreme and also reset the "old" main AirPort back to factory default settings

When the operation is complete, move the new AirPort Extreme over in place of the "old" main AirPort base. Set the old AirPort base aside and check the network to make sure that everything is operating as it was before with the "new" AirPort now operating as your main base station. You may need to power down the entire network first, then start up devices one at a time to check the network.

When you have verified that the new "main" AirPort is working correctly, then you can do exactly the same thing for each of the other two base stations......one at a time.....making sure that everything is working correctly before you set up the last AirPort base.

The potential downside......no one can guarantee that this will work correctly for you. It should....and it has worked for me when replacing one or more new AirPorts with a number of custom settings like port mapping, reserved IP addresses, etc, but your results may be different.

As best, all of the settings on each of the existing AirPorts transfer over to each of the new AirPorts. At worst, you wind up having to manually set up each AirPort with the custom settings that you want to use for each AirPort.

Bob Timmons's suggestion is a good one. Try that first. I have not attempted to use AU's "replace" feature other than for replacing identical models in kind, but that's what it is designed to do and it should work.

The only thing I find a bit annoying is when I plug in a new Airport device, every machine on my network that can see it, pops up the Airport Utility pro-actively. Very inconvenient when working with a network of over 50 macs!

You can avoid the pop up on each Mac, but you will have to change a few Preference settings in AirPort Utility on each Mac. It might take 30-60 seconds per Mac to make the changes, if you are interested.

On each Mac that you do not want to display pop ups........

Open AirPort Utility

Click on the AirPort Utility menu and then click Preferences

Uncheck all of the boxes