using unlocked phones with specific bands

Hey, guys, I'm new to these forums and honestly have been researching for hours and cannot still get a 100% answer on some of these. Basically, I got the ZTE Blade Z MAX... HORRIBLE phone. Crashes hardcore, receives less than half the texts, forgets the last app used and clears memory instantly, freezes, etc. It's garbage and I plan on getting a new phone from amazon and there are tons of "chinese" unlocked phones that are incredibly powerful with very good reviews. That way I can sell the ZTE and just get these. However, FAQs are vague on "will this work" because not only are those websites just not consistent with their information, I've literally found reviews of the phones they claim won't work and on a different video on youtube they show them running on Metro PCS. So, I'm learning the whole "bands" thing, 1/2/4/ etc.

Now, I know Metro uses T-Mobiles, which are here:
T-Mobile (and Metro PCS)
4G LTE Bands - 2, 4*, 12*, 66, 71
Frequencies (MHz) - 600, 700*, 1900, 1700/2100*

And I compared the ZTE's bands, which are 2/ 4/ 5/ 12/ 66.
Now, what is the minimum requirement? For one of those bands to work? Or is it more of a "the more bands the device covers, the more reliable connection" kind of scenario?

For example, here's a phone I was looking at:
The Huawei Honor 7x. Its bands are:
2/ 4/ 5/ 7/ 12/ 17.

Will this phone be compatible? And if it's NOT compatible with MetroPCS, could I just switch to straight-talk or cricket? I hear they are GSM as well and have great coverage in my area, so switching isn't the problem, neither is pricing. Just the phones here.