Reddit mentions of TRENDnet AC750 Wireless VDSL2/ADSL2+ Modem Router, 200 Mbps VDSL Downstream Speeds, USB share ports, TEW-816DRM

First, for a modem+router to work you need to receive service from a internet service provider (Cox, At&T, etc.) not from a mobile carrier (T-Mobile, Sprint). Do you already receive receive service from a internet service provider? Someone would be paying them a monthly fee and you would be receiving internet to your home from a cable/coax outlet or a DSL outlet.

Second, Nighthawk equipment is typically targeted to intense internet usage. Nighthawk's maximum capabilities will generally not be realized unless you are paying for the highest internet subscription from your ISP and also using multiple network-taxing PCs for gaming, livestreaming, and downloading. If all you want is faster internet for a few home devices like phones, you can use a cheaper modem and a cheaper router.

The first Nighthawk router you linked is designed for train stations and mansions with all smart appliances, not for typical home use. There's probably no reason for you to fork over $450 for it.

The second Nighthawk router you listed for 60 GHz, which means super fast speed but doesn't work outside of close proximity (like 10 feet). While 60 GHz chips have been developed, basically no commercial devices use them, only prototypes. I imagine 60 GHz will eventually be used for 4K streaming to smart TVs located near the router, but it's just not worth forking over $400.

Third, pick a modem that matches the speed of your subscription with your ISP. Here is a guide for picking a cable modem. Basically, higher DOCSIS version number (3.1 vs 3.0) and higher number of channels (32 vs 16 vs 8) means higher capabilities and more expensive. For typical home internet use, DOCSIS 3.0 cable modem with 8 channels is plenty. This is the type of cable modem I have, and it supports my 100 Mbps internet subscription. A DOCSIS 3.0 cable modem with 8 channels should be about $50. If you really want to make sure you match your internet subscription, you can get a DOCSIS 3.0 cable modem with 16 channels for about $80-$90. You probably don't need the Nighthawk DOCSIS 3.1 cable modem with 32 channels that you listed, which is about $150.

Here is a guide for picking a DSL modem. Basically, a VDSL modem has higher capability than an ADSL modem. An ADSL modem might not be fast enough for your typical home use, but you can get an ADSL modem for about $40-$50. VDSL modems should work for your typical home use. VDSL modems are usually sold a as a combination modem+router, rather than a standalone modem. You can get a VDSL modem+router with a faster router half for about $120+. You can get a VDSl modem+router with a slower router half for about $70.

Fourth, pick a router that suits your home use. You want a router that (1) has fast speed and (2) has enough range for a signal to reach you based on your home size. Here is a brief guide of routers speed. Basically, WiFi "AC" protocol is the standard for home use, and higher numbers after the "AC" (AC 1900 vs AC 1750) means faster speed. AC 1200 routers are typically about $405-$50. AC 1750 routers are typically about $80. AC 1900 routers are typically about $120. You might notice the speed difference between 1200 and 1900. You probably won't notice the speed difference between 1750 and 1900. Anything above 1900 you probably won't be able to tell the difference.

There isn't really a guide on router range. Router manufacturers have collectively agreed not to advertise their signal strengths. So you have to look around the internet for reviews, or do your own tests. You can do you own tests by buying multiple routers, using any of the millions of free Wi-Fi strength apps on the app store, and returning the the routers with lower strength. I tested some routers this way and ended up keeping this router.

I prefer standalone routers. They sometimes perform better than combination modem+routers because designers didn't have to worry about incorporating a modem. Also, I can swap them out without having to buy a new modem. However, you can also buy a combination modem+router to save space. But make sure the modem half matches your internet subscription, and the router half matches your home use. By paying for a decent internet subscription, matching my modem to the internet subscription, and matching my router to my home, I have the best in-home WiFi of any of my friends.

EDIT: Fifth, wait for Black Friday and Cyber Monday electronics deals. Electronics usually go on sale the weekend after Thanksgiving. You might be able to pick up compatible modems and routers for cheaper.