If I were trying for light weight, I would start with the design. I would start thinking about all the design tricks I know that provide strength with minimal material. Use "L" shape legs, or drill or hollow them out. Thin everything that doesn't need to be thick. Consider a thin top, but use battens (thin strips on the back), or a thicker rim to provide strength and support. You might even think about making a torsion box, with thin layers on top and bottom and a simple structure between them to hold it together. Wrap it in veneer strips to give it a nice look. I wonder whether 1/8 inch plywood is too thin for the top, if properly supported?
With the right design, you may be able to achieve the light weight you desire, but be able to use stronger, better, nicer wood species, maybe a hardwood.
By the way, for beginners, "SPF" stands for "Spruce, Pine, Fir". It is the white softwood construction lumber that you find at the big hardware stores, where you don't know the exact species of wood, but you don't need to know, either.