The foundation

The first big hurdle in the planning of the house is what type of foundation to settle on.  There are many options as I already stated, but I think I have settled. 
I have decided to do posts with a footing under each, but first to consider is how to cover the foundation posts to exclude cold air(as much as possible) from the underside of the house.  I will have to put on a skirt.  It will be pressure treated plywood.  I do not plan to use pressure treated plywood for structural support.  But the skirt will last a long time in pressure treated.  The skirt  must be seamless from the sill of the house to below ground level.  This may be a problem if I put posts directly under the walls of the house.  There would always be some concrete footing protruding from the plane of the sills, as there has to be good pressure from the weight of the building on the center of the post.   So, there is one option to get around the bulge. 
If I make the posts(piers) in three or four rows at about 6 inches(just a random number) inside the finished perimeter of the house, then lay three or four beams on top of the three or four rows of posts to the finished length of the house perimeter(rim joists), and the rim joists and floor joists beyond the side beams to the finished width of the house and the ends of the building on the very ends of the beams, then there will be downward pressure of the house's weight from the outside walls that will sort of lever the center of the house upward a bit.  Basically I will be building like the old garrison houses where the upper story protruded a few inches and the levering up of the middle made the center of the house less bouncy.  Did I explain that well.  I will ponder a way to explain better.

In this image, the rim joist labeled overhangs the beam(coming forward toward you) by several inches.

 

 

Lets just say as a "for instance" that I put a row of posts to a total of 25 feet, a little shorter than the house.  Then place heavy beams on top of the posts to a total of 26 feet which is my final length of the house.
The three rows of posts will be a total of 17 feet apart on the width of the house which will eventually be 18 feet total width of the house.
The rim joists at the gable ends will be flush with the ends of the beams, and in the other direction the floor joists will rest across the three beams, protruding 3 or more inches over the beams and the rim joists on the ends of the floor joists will total the 18 foot width of the house.  The side rim joists will be almost floating beyond the beams below. The weight of the building would be on the floor joists.
Now, the gable ends are supported by the beams below,
The side walls may have a wooden post scabbed onto the side of the posts and support the floating wall a bit more than just the leverage.  This would also become nailing surfaces for the skirt.
Whew. 

 

 

This may need refining, for instance, I may bring the concrete posts just up to ground level and from there up to the beams use 6x6 or larger pressure treated to support the beams.
In every instance there must be a separation between the top of the concrete and the wooden components.  In this instance, the bracket sunk into the concrete does that job.
You could also run the concrete foundation all the way up to the beams, but I am trying to save money, and I believe that the 6x6 post will be cheaper than buying longer Sonotube and filling with concrete.
What is not shown here is a series of diagonal braces that must be put on every 6x6 post bolted from the base of the post to the beam and in the other direction into the rim joist.  There are metal strips that can be used for this, but it is common to use short mitered lengths of 6x6.
All instances of use of metal in the foundation assumes that there have been steps taken to assure that moisture will not affect the metal(good drainage and or ventilation in the summer).  A door can be put into the skirt and or vent grills(covered in winter).

Diagonal bracing is absolutely necessary because the wind or earth tremors, etc. can easily push the house to the side, and you could find your house sitting on the ground next to your foundation.(Timmmberrrr)