If its on his property line and there is no easement then the only thing you can do about it is flip him the bird when he drives by.

Inside of a property line would be the area that the perimeter of the property encloses. If you draw a rectangle on a piece of paper the area inside the lines would be the same as the inside of a property line.

Not necessarily.

Property lines are established by surveys. The sidewalk may be one of the fixed points they use to establish the location of the property line, but otherwise it is unrelated to the property line.

The fence cannot be outside your property line.

Yes.