I agree with
@getrealbro that the Optimum WiFi Router may not be necessary, and might be an added cost if you are renting it. ISP provided router often broadcast a "Guest" WiFi so other Optimum customers can use your WiFi... which could slow your internet speeds down.
The 3rd Gen Extreme and Express (depending on version) are dual band 2.4/5GHz, but 5Ghz is 802.11n so max speeds on these WiFi access points will be no more than 150-300Mbps, probably ok unless your ISP service is faster. The Time Capsule, depending on version may be 802.11ac which can attain speeds up to 1300Mbps. Depending on the size of your home, the Time Capsule may be enough to cover the entire home.
I would be more inclined to use Apple gear only. And, keep in mind, less is usually better when it comes to WiFi access points. So, start with removing the Optimum WiFi router, and setup Time Capsule as the router for the home. Take the AP Extreme and Express offline and test WiFi signal throughout the home. If you get good coverage, leave them out of the picture.
If the upstairs signal is weak, use the Extreme with the same SSID and password as the WiFi on the Time Capsule. If, and only if necessary, add the Express back into the mix.
As for SSID, using the same on all simplifies things. But, depending on what kinds of wireless devices you have, it might make sense to name 2.4 and 5Ghz different SSID (NETWORK & NETWORK5G). For example, if you have a number of older devices, cameras, etc that can only use 2.4, but have some newer things that can use 5Ghz, splitting the SSID can reduce the number of clients connecting to 2.4, resulting in faster speeds on each band. So, for 5Ghz capable devices, only setup the 5Ghz SSID.
The thing to keep in mind is, 5Ghz has shorter range, but faster speeds. So, for an iPhone for example, the 5Ghz might be preferable, but the signal might not be strong enough to reach outside, garage, etc. So, these mobile devices that typically roam to the outer reaches of the 5Ghz range, setup both SSIDs so they can switch when needed. They will tend to use the 5Ghz, but might stay on 2.4 as you roam about since it is more stable to stay on the same network.
The fact that you can use Ethernet to connect all the essentials is a big plus. Ethernet is generally a better solution due to less interference and more stable connections. As far as adding extra access points, ethernet is the way to go to connect them to your network, else you lose a lot of speed and capacity.
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One other question...When I create a “roaming network” where all the wireless access points (Airports) use the same Network Name and Password...how does it know which Wifi I am connected it to? For example if I am in one part of the house and connected to the TimeCapsule but then move to another part of the house where the Airport Extreme has a stronger signal how will I know it connected to the stronger wifi? When I had them as different names I had to manually connect in order to access the one with the better signal strength.
Generally, you don't care. The OS considers signal strength, speed, and persistence. If you move to a place where a stronger signal exists, but the signal from TC is still viable, it may stay with TC to keep your connection intact (persistence). But, if there is a big difference in signal strength, it should automatically change to the Extreme.
