OK, that model number is for the old “connect home“ Wi-Fi mesh hub. That model has been discontinued.
The newer model is “Samsung WiFi Router with Plume,” model number ETWV525. It can have up to 32 sub hubs. However, it is not compatible with the model that you currently have, you would have to completely replace both the primary hub and the sub hubs with ones of the new model.
You can tell the difference because the newer model has two logos on it, both Samsung and smartthings, and the model that you have has only one logo.
Are you aware that Samsung has decided to take smartthings out of the home automation hardware business? They are transitioning to partners who will build “works as a smartthings hub“ Devices. Smartthings will offer the cloud and the app, not the hardware. So we don’t even know if a Wi-Fi mesh version will continue to be offered. It has already not received firmware updates as often as the other hub models.
Official announcement:
An Update Regarding our Hardware
At this point, over 95% of the smartthings customer base isn’t using a hub at all. They have a Samsung smart television or appliance and maybe a dozen Wi-Fi devices and a hue bridge and that’s about it.
Honestly, for a house of that size you’ve really moved out of range of what smartthings is intended for. Or most of its competitors. Most people would be looking at Lutron Homeworks or Control4 instead, although obviously those are much more expensive.