It looks like you are more comfortable with metal fab but wood is easier to work with. The basic plywood buck is soo much easier to create & modify. Any experienced FG fabricator are familiar with styling bucks and can assist you with the creation of your FG body sections. Even before creating these bucks, depending of your CAD/CAM experience all of your work could be kept in database & be tested with many different fluid flow programs. There are tube chassis design programs to help design a balanced, lightweight yet strong structure. A lot of your assumptions can be easily tested and a whole lot of fab time saved.
Car Body Buck in Plywood