you would be better off by breaking this up into 3 different threads. Asking all those questions in one thread becomes a distraction. You'll get more answers with it broken up.
I'll jump in with #4. There are two electric systems in you trailer. the lighting is a 12 volt system run by a CONVERTER. It changers 120 volts to 12 volts. You will find a 12 volt fuse panel. You also will use 12 volts as a control circuits for your refrigerator, furnace (which you seem not to have), water heater, range hood. You will also have a 12 volt battery which is charged by the converter.
Your wall outlets are 120 volts. They are controlled by circuit breakers just like you house. You will find a GFI circuit device in the bathroom. It will control all receptacles in your trailer that are within 6'of a water source and also outside outlets.
You probably have a 30 amp 120 volt Electric service. That is a one leg 120 volt to your breaker box to a 30 amp single pole breaker. Your breaker box will be located rear the floor. Your roof A/C is 20 amp 120 volts. There won't be any 240 volt devices in your trailer.
Water heater will probably 120 volt and/or gas. Refrigerator will probably be electric and/or gas.
A tongue jack will be 12 volts. slides will be 12 volts. Roof vents will be 12 volts.
Make very sure your electric husband under stands the you shore power cord is 30 AMPS 120 VOLTS 3 wire. NOT 240. It looks like a 240 dryer plug. It is not.
Schools out for today;)