Hillside woodframe building

[tigatgu]

I need to prepare a structural calculations report for a woodframe multistory house on a downhill terrain.

The cross section can be described as below:
·Existing ground is 2 horizontal / 1 vertical sloping down and away from the street.
·Assuming the street is at elevation 0.0 Ft.
·The second floor (20’wide x 20’lenght x 8’height) is at elevation 0.0 Ft, and 20’ away from the street.
·The first floor (20’wide x 40’lenght x 8’height) is NEXT to the second floor, and is at elevation -4.0 Ft (minus 4')
·The third floor (20’wide x 40’length x 8’height) is right above the first floor, so is at elevation 5.0 Ft

Questions are:
- How should I analyze the horizontal diaphragm? Should I treat the structure as a 3 stories house or should I separate the second floor from the first and third?
- What lateral force resistance system (masonry blocks wall, steel bracing…) below the second and first floors should I use? Note that the difference in elevation between the second floor and the existing ground is 4 Ft – 14 Ft, and between the first floor and the existing ground is 10 Ft – 20 Ft.
- What kind of material (steel, wood, or concrete) would be best for the column below the second and first floor?

I am looking forward to read any expert input.
Thanks