Powering and signal for MAX Transit CAT18?

Good evening. I have installed the MAX Transit CAT18 router in my travel trailer and hardwired it to the 12V system so it is powered while we are towing it behind us. I have a couple other power options and had some questions:

  1. I think I read on another post, that I can have multiple power options all connected at the same time…is this true? If so, will it always pull from the strongest (i.e. best) power source? Will I get better transmit power (i.e. distance) with more power (say when we are plugged into campground power and have 120V available) or when I plug it into 2 USB jacks?
  2. Based on the hardwire kit from Pepwave (which I was unable to order) it appeared to be an inline 3A fuse…is this the correct amp fuse?
  3. The 2.4GHZ band doesn’t seem to be broadcasting? What am I missing?
  4. What should I be expecting for signal strength and distance? I’m an currently reading about -70dBm at about 20 feet?

Thank you!