Question about Huawei E5576-320 Mobile wireless network equipment

No! This version does not work in the USA / North America and parts of Central / South America, for example.

Unfortunately, I have just experienced this myself...

Clearly not, because this modem only covers a selection of frequencies. You usually achieve much better coverage with a smartphone that you can use as a hotspot.

The Huawei modem has this frequency coverage, so if they are used in the destination country then it works, but it can be tight with 3G UMTS.

UMTS frequency 900 MHz, 2100 MHz
LTE frequency 700 MHz, 800 MHz, 900 MHz, 1800 MHz, 2100 MHz, 2600 MHz

Yes

Yes