Yes, it works very well.

Yes, I use this router in my remote cabin with 12 volts, I don't know the exact size of the plug, but it is the most commonly used plug. However, it is important that the plug is fused (small glass fuse) and not connected directly to the car battery.

5G is not supported

Hello. Unfortunately, I don't know. I don't need it either. Greetings

According to my information, this device reaches up to the following speed values: Download: 150 Mbit/s Upload: 50 Mbit/s Of course, this depends on the SIM card package that you take out with your network provider. In terms of reception, the device should generally have a more stable and better reception than a smartphone.

No that is not possible

Hello Grosskopf Yes, you can connect an external antenna. I have always ordered this https://www.digitec.ch/de/s1/product/delock-lte-antenne-mit-sma-stecker-mobilfunk-antenne-netzwerk-zubehoer-5741667. Greetings

I have this router in operation and work on LTE Band 20 (800Mhz)

According to the manufacturer, you can use the SIM card of any provider.