A phone as a home 4G modem/router?
That's not a bad idea at all. I have Verizon Wireless and I do this all the time. That's what tethering is for, and the USB option as well. 4G is fast, and for what it's worth, based on what you've said, it seems like a fantastic idea.

To answer your second question and forward, no - -  your phone wouldn't fry, providing you got a phone with good specs. 

As far as I'm concerned, they have been more reliable than regular average routers. It's LTE after all, so it's not a surprise. Can't speak about the throttle, that depends on T-Mobile and their terms. I think they do throttle, but it's not a huge difference. 

I'd recommend talking to someone from T-Mobile and asking them what device has best specs and battery power. Also, you can get a data monitor to monitor all traffic and block / allow certain connections via incoming addresses or devices. Those apps are available on Google Play so let me know if you need them. 

I have a family member who uses T-Mobile tethering  amongst six devices at home, two of which are a PS3 which plays Netflix and it's not slow at all. Randomly given of course, every server has ups and downs.