how to set up wifi repeater

The Express name does not show up in my wifi list, only <…home> and <…home 5Ghz>, which is pretty much useless.

Sounds like you are confused. In an extended network, you will not see two networks, you will only see one signal, since both AirPorts are broadcasting the same wireless network name. Since it appears as if you assigned a different name to the 5 GHz network, you will see two networks when you click the WiFi menu.

If you use a utility like WiFi Explorer or WiFi Scanner then you will see the two networks that each AirPort is broadcasting.....two using the normal name and two using the 5 GHz name(s).

Wireless devices will pick up the signal from the closest AirPort. You can't dictate to which AirPort a wireless device will connect.

I have four AirPorts here, but I only see one wireless network when I check the WiFi menu at the top of the screen. Yet, if I open AirPort Utility and click on any given AirPort, then I can see the "wireless clients" that are connected to that AirPort. In the example below, you can see the "wireless clients" that are connected to my Time Capsule.

If I wanted to see which devices were connected to one of the other AirPorts, then I would click on that AirPort.

Your Mac laptop will usually automatically "switch" to pick up the signal from the closest AirPort. Unfortunately, iPhones and iPads will usually not do this. To get the iPhone or iPad to pick up the signal from the closest AirPort when you move the device, you will need to get in the habit of temporarily turning off the WiFi on the iPhone, then turn the WiFi back on when it is near another AirPort, and it will usually pick up the signal from the closer AirPort.

OK, thanks. I'll assume that they have been updated with the current or recent firmware versions.

Here is how to get the AirPort Express setup to "extend" the wireless signal from the AirPort Extreme:

Power off the AirPort Extreme, wait a few seconds, then power it back up again.

Temporarily, move the AirPort Express to the same room or close proximity to the AirPort Extreme

Power up the Express for a minute or two

Hold in the reset button on the side of the Express for 7-8 seconds, then release and allow the Express to restart to a slow, blinking amber light status

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

Click directly on AirPort Express under that listing

When you click on AirPort Express, that will get the AirPort Utility setup "wizard" up and running. It will take a few seconds to analyze the network and suggest the correct setup for the AirPort Express. The window will look similar to the example below, except that you will see your devices displayed along with the name of your wireless network.

Type in a name that you want to call the AirPort Express

Click Next

The setup wizard will configure everything for you automatically. When you see the message of Setup Complete, click Done

Power off the Express and move it to a location that is about half way between the AirPort Extreme and the general area where you need more wireless signal strength and speed.

Power up the AirPort Express and you should be all set. The more that you have line-of-sight between the AirPort Extreme and AirPort Express, the better the network will perform.

Depending on the number of walls or other obstructions in the signal path, you may need to experiment a bit with the location of the AirPort Express for best results.

I kept the Netgear modem/router and decided to use that. Trouble is, I haven’t found a coherent set of instructions on how to do that

There are no settings on the AirPort to allow the Netgear.....or any other brand of router for that matter.....to wirelessly "repeat" or "extend" the signal from the AirPort, so if this is even possible, everything must be set up on the Netgear product.

If the Netgear product requires an Ethernet connection for its setup, then you could use a Thunderbolt to Ethernet adapter to accomplish that task with your MBP. Thunderbolt to Gigabit Ethernet Adapter - Apple

While it is possible.....but also unlikely.....that a user on an Apple support forum might be able to tell you how to configure a Netgear product.....or confirm if this is even possible.....you will likely receive a much faster and more informed response to a Netgear question on a Netgear support forum.

Apple has designed their wireless "extend" or "repeat" feature to only allow other Apple products to be compatible with each other, so my opinion would be that it is doubtful that the Netgear product would be compatible with an Apple product to do what you ask.

The Netgear product would probably work if you could connect it back to the AirPort using a permanent, wired Ethernet cable connection, but here again, this is a question for a Netgear support forum.

From what you are saying, Apple routers can’t be used to extend wifi coverage.

They can if you are using Apple routers with each other. But, the AirPorts cannot wirelessly "extend" or "repeat" a signal from a third party router.

Whether or not the Netgear would work with an Apple product is open to question. My opinion is that it would not be compatible with an Apple router for the feature that you are looking for.

If the roles were reversed and the Netgear was your "main" router and you wanted to wirelessly extend or repeat with the AirPort, then it would be all up to the AirPort to do this, so it would make sense to ask about this on an Apple support forum.....not a Netgear forum.

What model of AirPort Extreme do you have? Is this the "tall" or "tower" shaped version, or one of the older "flat or square" versions of the product?

What model of AirPort Express? It sounds like this is not the current two-Ethernet port version and is an older one- Ethernet port version. Look on the side of the Express in the fine print to find the model number. It will likely be either A1084 or A1264. Hopefully, it is A1264.

If you have been using the AirPort Extreme, then chances are you have applied firmware updates as they became available. The current version is 7.6.8.

AirPort Utility in Sierra requires that the AirPorts are using firmware version 7.5 or higher. Once you have the AirPort Express setup, then we can check to see if any updates are available.

Edit to post above......

Sometimes, when you move them, iPhones or iPad will switch to another AirPort after a few minutes, and sometimes they won't. If you want to give the iPhone or iPad the best chance to pick up the signal from the closest AirPort, temporarily turn off the WiFI on the device, wait a few seconds, then turn the WiFi back on.