it's close, and it will work, if you make suru the 3/4" bottom panels
are well attached 4 sides to a rib and that that rib is well bonded to
the top.

So screws driven between the plies will not compromise plywood's
strength to any significant extent and will not separate the plies
from the weight, right?

Good quality plywood stringers will be far stronger around the corners
than hardwood. Plywood has many plies with alternating grain direction
to carry the load. A hardwood stringer would have some directions that
aren't as strong as the others. The stability of the plywood will also
help the joints and bonds last.

I'm very glad I asked this group before I started the project! The
torsion box design you guys suggested is MUCH better than the amateur
one that was brewing in my head.

Is Bondo still my friend to fill in fastener holes, joints, and other
voids before painting?