But, I don't know what a reasonable amount to pay him for this work.It is a single story about 1000 square feet, rectangle with vinyl siding. 

For example, a large square, a rectangle half the size of the square and a small sqaure half the size of the rectangle.

First, I would make sure that the 3 acre lot is NOT irregular (square, rectangle, and trapezoid are best).Secondly, does it have a good water well and electricity near the property?

All squares are rectangles, but not all rectangles are squares"  

Survey showed a perfect rectangle, but the fence was at an angle.

It depends on the specific properties within specifically analyzed micro-markets, executed using specific strategies where the analysis generated profiles match the criteria of your REI plan, at the current timeline in that plan.Or, another way to say that is, "All squares are rectangles, but not all rectangles are squares"

This way if you have renters that only need 4 rooms you could rent that part of the house plus the living room and kitchen, and have a door locked that would access the other side that will not be rented.2/ Have amenities that short term renters are looking for;Jacuzzi on a terrasse,  basement with a movie room, PS4 Setup, Ping pong, maybe a sunken rectangle full of cushions in front of the TV. 

I'm seeing a lot of houses with diagonal rooms (instead of square or rectangle) is that normal? 

I drew the red rectangle island in the mid of the kitchen and asked if my contractor can run the pipes from the kitchen & bath (in the right) from the floor (I am pretty sure the joists run this way).

The compressor units for mini splits are awesome- quiet, power savvy, and small, you can tuck them in and hide the easily.  3) I'm not HVAC experienced, other than casual interest, but I've seen on This Old House the installation of smaller 4" ducts that run to a smaller room "port" that is circular, instead of a big vented rectangle.