sandy soil foundation requirements

Sandy soil is very easy compared to expansive clays. However, you will need to use perimeter 'grade beams' and similar intergrally poured 'beams' under all load bearing walls.

Dimensions of the beams depends entirely on the the weight of the structure.

As a minimum,use 4000 psi concrete, 6" thick slab, with 1/2" rebar every 1' in crosshatch pattern for the slab, and a 'cage' of similar rebar with 6" spacing all direction in the 'beams' with rebar min of 2" from any surface of the beam. Perimeter beam of 12"wide x 18" deep (in addition to the 6" slab thickness) will carry 2 story brick facade structure. Interior beams proportionally sized for loads.

A competent civil structural engineer can provide you a better design

You should consult a civil engineer competant in the design of the type of structure you are planning and local building codes. There is no simple generic design criteria, the building code is about as simple as it gets. You may need a geotechnical investigation and a competant foundations engineer. You probably do not need a structural engineer for a 2-story building, except under special situation, uses, or local requirements. Talk to your local building department about requirements. They may have specific requirements and all you need is a licensed civil engineer. A few things to consider are: Where is historical high groundwater below the proposed structure? Are their liquifiable sands? Is the subsurface stratigraphy variable between compressible deposits and sands? Is it shallow soils over hard rock? What seismic zone are you in? What is the importance factor for the building? What are the LL, DL, Wind, Snow, and Seismic loads? Also symmetry of the design?

4000 psi concrete seems a little high for most common 2-story structures. You would want to consult a local civil engineer on this, but i think 3000 psi would be more common. A 6" thick slab might be a little thick, you could probably use a thinner section, but for #5 rebar reinforcement in 1 mat you will need at least 4" over clean cement sand. Also #5 rebar on 12" spacing is pretty common, but could be insufficient, or in some places excessive. Someplaces allow WWF for slabs for many residential applications.