@jennylas ive nevr used powerline, and i dont see why you would need to run it in your scenario as i think a regular deco kit would cover you. what speeds can you (or do you) get from t-mobile straight from the router? you will see speed degredation through wireless only backhaul. i reluctantly ran cat6 cable by pulling existing cable tv coax thats unused and thats helped out tremendously. but that also depends where your main router is. since its a 5G modem, can it be placed anywhere in thr house? will you be disabling its routing capabilities or using the decos as access points?

  @dictoresno  I'm still figuring out the T-Mobile set up at the moment. There are a few settings I need to test tomorrow to see if this is even feasible at our place. When we did field tests around the house with a phone on a T-Mobile network, we were clocking in at 500-600 Mbps in a particular spot. I don't expect those speeds on the 5G Business Internet, but we were getting like 9 Mbps earlier. Something is definitely up and we may have to go with another ISP if we can't figure it out. Typically, speeds for internet around this area is 50 Mbps max, usually less. We currently have around 20 Mbps with our AT&T Fixed Wireless. So, a wireless only backhaul may not be the best solution for us. For 5G, you technically have to find the best position and have it face the tower directly. Unfortunately, the coax cables are in different rooms than where our "best spot" is.  My plan is to set the Inseego as IP Passthrough.

  @jennylas I think one of the most important things you were going to need to know first is what kind of download speeds you're going to expect. Because that may determine what your next course of action is going to be. If you do not have a lot of bandwidth, and then start adding wireless access points with wireless backhaul it's just gonna keep splitting that bandwidth up until you have nothing. 
 

I was under the impression that a lot of these mobile 5G routers were completely wireless and ran off of a Sim card and did not need any kind of coax. 

  @dictoresno yes, that is correct. No coax needed, but you need to have it facing the cell tower directly. Radio signals are also really super finicky when it comes to obstructions. It doesn't like being around metal. Most of our windows have a type of gas for insulation and I found out, that it quite literally cuts our download speed by 15x. We have a glass door leading to our balcony and that clocks in at 500-600 Mbps, but if I move two feet to the left in front of that insulated window, I'll get around 40 Mbps. So, yeah 5G doesn't need a coax, but it's super sensitive to placement. I mean really we could just get an external antennae or an outdoor modem/router (like the Inseego FW2000e) and we would have way better options for placement, but both of those options will run me at least $800 because the FX2000's compatible external antennae are limited to certain bands that unfortunately we are not on. We would have to get an external antenna and new modem/router. The FX2000 is free with T-Mobile. The only other options they have are their trashcans that are notorious for CGNAT causing double NAT issues. 
 

If we can fix this current issue with the FX2000, I would expect at least 1/4 of the phone test so maybe 125 Mbps dl off the router. If we have to stick with other options around it, maybe 30 Mbps off the router. I would be happy with 50 Mbps throughout the house, but will settle with what we have now at 20 Mbps.