This varies each install but typical 1-2 days for the electrical aspect and then we return after the fuel source is hooked up to program.
Standby generators have automatic transfer switches that monitor the feed from the utility company and when your home loses power it will automatically turn on. When it gets power back from the grid it will automatically turn off.
Yes, ask the technician when he is programming it.
Yes, simple maintenance is required and is required to maintain all warranties.
Generators can be fueled by both natural gas and propane.