T-mobile gateway with seperate router

I was considering the same setup you have when I first got my gateway, but I decided to see just how good or bad the Arcadyan KVD21 5G gateway performed before I connected my existing router.

The first trick during setup is to name the network(s) on your new gateway the same as your router. So, if your SSID was named PickleJuice on your old router, give the new network the same name. Devices on your network should connect automatically and not know the difference. You can do this very quickly using the T-Mobile phone app under the Network tab.

As for DNS, I handle that at the client level, not the router. What often works for one device doesn't for another, and so I do not change DNS on the router, but that's a personal preference.

As for a guest network, I used the T-Mobile app to create a new network (PickleJuiceGuest) with a different password and that is the only network you have to let your guests use.

The wireless reach of my Arcadyan KVD21 5G gateway is surprisingly good, and I don't see much difference between my TP-Link AX50 and the T-Mobile gateway. I still need a WiFi extender in one part of the house, but I needed that with the original network as well.

There is, of course, nothing wrong or incorrect with what you're doing. It drives most of us on the forum crazy that the gateway can't be configured or worse, there is no way to connect an external antenna to boost the T-Mobile signal. I just want to eliminate as much complexity from my home network as possible, and having only one device instead of two is part of that philosophy.