jike I like your idea but, I suggest to also include 4 sides connection with dowels to put all existing footing in total interaction with the new top and side concrete. Is very important to install the dowels with the Hilti technical recommendation books accordingly with the footing moment...
Is important to consider the moment acting in the concrete foundation wall for the slab loads reactions, to prevent future problems on the concrete foundation wall.
It system have it limitations parameters by the ICC, please visit the following Web page:
http://www.superiorwalls.com/pdf/builder_pdfs/21-72.pdf
Is very important to verify in your local area if you require the UBC97 parameters or if the ICC is the accepted code at your local area.
Other...
Is important to consider the most critical case, I recommend to use the 1,000psf soil bearing capacity for the footing designs to guarantee security and prevent future settlements problems. In my opinion the use of most critical situation is a good guidance in combination with the codes...
You can model this structure using shear walls in staad ,but also you can use pin points connections at the concrete core structure at slab and beam points to idealize the shear reactions acting on the shear walls at each building level. With it horizontal and vertical shear reactions you can...
When you perform a seismic analysis for a light steel construction you need to consider the modulus of elasticity of the material, also you need to consider the fatigue analysis at the connection points in the structure. Typically is recommended to evaluate it kind of structure using a moment...