Since you have no code to follow, you have a lot more flexibility than most people have, who are required to follow code. In your case, you may be able to save costs by designing each major framing element based on principles of mechanics rather than code books, which sometimes require overdesign of the structure.
Generally speaking, long horizontal members such as beams, joists and rafters are designed based on bending strength. Bending is typically controlled by uniform loading on the member (pounds per square foot is typically what is listed in the code book). You size the member based on bending strength, and allowable deflection. Code usually specifies minimum loading for a floor, for example 30 psf for a kitchen, 40 psf for a living room are common loads. You may want to design for lower loads, if you are confident you know what is going in a specific room. Code typically also specifies a minimum stiffness (deflection divided by length), which may also not be applicable to your situation.
The same applies to beams. Stud walls are pretty typically designed 16 inches on center, not because of strength, but generally because of considerations about installation of sheet rock or plywood. In your case, you may want to vary from standard dimensions.
What I am suggesting is that since you are not code driven, you may want to consider working with an architect or a designer, who may be able to save you some money on framing, foundation, and interior fit out, based on actual principles of engineering and intelligent design practices, rather than following a code book for your project.