Using airport express as router and another as extender?

Two AirPort Expresses will do exactly what you want. One Express will need to connect directly to the modem/router using a permanent, wired Ethernet cable connection. The second Express can wirelessly extend the network from the first.

Keep in mind that the "extending" Express will need to be located where it can receive a strong wireless signal. Line-of-sight between the Expresses would be ideal, since any obstructions in the direct signal path will slow down the network.

A normal wall will slow things down by 15-20% or so. A ceiling will slow things down by 30-40% of so, since a ceiling on average is usually about 3 times more dense than a wall. You get the idea why you want to have line-of-sight as much as possible.

If you are after top performance, you will need to wire the second Express back to the first, since there will be no signal loss through the Ethernet cable up to 300+ feet, or about 100 meters.

You can probably leave the WiFi on at the modem/router.....in case you want to have a separate wireless network for "guests' or the kids. Or, turn off the WiFi on the modem/router if you don't need another network.

I just got off talking to two Best Buy support teams and both of them said that the Airport Express (or even with using one Extreme and Express) will act like a PowerLine extender. Meaning, if I have my HOMENETWORK_5G SSID from my current router then using an Airport Express upstairs would create a different SSID so that I would still have the same problem having to switch between SSIDs.

This is not correct. By default, the Apple extender will provide the exact same wireless network name and use the exact same password as the "main" AirPort, as long as you use 2 AirPorts. This is true no matter whether you connect the AirPorts using wireless, or using a wired Ethernet connection.

They informed me that the Google - Google Wifi AC1200 Dual-Band Whole Home Wi-Fi System and the eero - AC Whole Home Wi-Fi System are the only options in which it will be a true extender of my SSID (network) and not have the problem of different SSIDs to connect to when upstairs to get better coverage. Are you aware if this is true?

See my answer just above. I don't know on Eero or Google since I have not tested either product. I do know for a fact that there are any number of routers that can be configured to provide the exact same wireless network name, password, etc in extended networks. Cisco, Linksys, ATT, Asus, etc, so the Best Buy folks are imagining things if they think otherwise.

If I got either the Airport Extreme/Express or the Eero or Google wifi packages, then when I use an ethernet cable to plug the picked router into the now motorola router, am I still able to have the TV, apple tv, and PS4 hardline/ethernet connection to internet through it's ethernet cable to the motorola modem

Yes, with an AirPort Extreme or AirPort Express. I don't know on Eero or Google since I don't have either of those products here to test.

I read this as my 5GHz signal is still being used and just enhanced/extended with the airport express and NOT being the airport taking the 5GHz signal and then making another SSID based on the signal and extending it that way.

That is correct. Both AirPorts provide a network that uses the exact same wireless network name(s).

But, I would caution you regarding 5 GHz. These signals are weaker than 2.4 GHz signals, so 5 GHz is only going to work well when your wireless device is close to the router, or it has line of sight to the router. That is why I am stressing the importance of your extender having line of sight to the main AirPort....so it will connect using 5 GHz. Otherwise, the extender will connect using 2.4 GHz, since that is a much stronger signal.

If your extender does not have line of sight to the main router or very close to it, then you should wire the AirPorts together using an Ethernet cable. Better yet, wired them together anyway, and then you will know that your network is performing at its best. That is the type of setup that I use.

However, upon setting up the wifi (which I spend an hour with Netgear support in setting up), they informed me that there is no way to EXTEND my current HOMENETWORK_2.4G and/or HOMENETWORK_5G networks. Instead, I now have two more SSIDS (HOMENETWORK_NETGEAR2.4G and HOMENETWORK_NETGEAR5G)

If Netgear support has told you that there is no way for you to do what you want your network to do, I would take them at their word.

If you want to try 2 AirPorts, and you buy from Apple, you have 14 days to return the product for full credit or refund if you are not satisfied. Other stores and other manufacturers that you might be considering may have similar policies.

Apple's default setup will assign both the 2.4 GHz and 5 GHz signals to use the same wireless network name. Your devices....if they are capable....will automatically connect to the signal with the strongest signal. This makes things very simple, and it is the simple setups that always seem to be the most reliable. This is the type of setup that I have used for years. The only problem that I've ever had was that relatives want to visit just to use the wireless.

It involves a few more clicks of the mouse, but you do also have the option to assign separate names to the 2.4 GHz and 5 GHz signals if you want to go that route. I don't use this type of configuration, but some other users swear by this type of setup. And, other users just swear when they try this, because they don't want to be bothered with selecting from 2 different wireless network names on each their devices.

In either case, whether you have both 2.4 GHz and 5 GHz signals using the same wireless network name, or you want to have a separate name for each of the 2.4 GHz and 5 GHz signals, the "extending" AirPort will be a mirror image of your main AirPort.

Downsides to considering 2 AirPorts......It has been 5 years since Apple introduced the Express and their plans for future products are not known. If you want to go with the latest technology, that would not be Apple.

Correct.

Now, for a few checks to make sure that the network will do what you want, performance wise. The AirPort Express has 100 Mbps Ethernet ports, so the top speed that the Express can ever provide over wireless or wired connections is.....100 Mbps.

That will not be an issue if your Internet connection plan is 100 Mbps or less. But....if your Internet connection plan is faster......300 Mbps for example, as is my plan with Spectrum, then the Express would be a poor choice, since you will be giving away two thirds of the performance capability on the network.

An AirPort Extreme, which will easily handle 500+ Mbps Internet connections would be a much better and obvious choice.

Next item, the USB port on the AirPort Express will only support a compatible printer. The USB port on an AirPort Extreme will support a printer or a hard drive, if you were thinking about network data storage.

The wireless antennas (6) on the AirPort Extreme are all located right up at the top of the "tower". The wireless antennas (4) on the Express are inside the device. Not too difficult to figure out which AirPort will provide the better wireless speed and range.

I think you already know the answer. It all depends on whether you plan to upgrade your Internet connection plan/speed. If not, then two Expresses would be fine. If yes, then two AirPort Extremes would be the way to go.