Nic, call me paranoid about wing bolt plates pulling out, but if the 1/4" ply plate isn't keyed into cutouts in the saddle doubler I would -and this is just me - drill 1/8" holes through the outside of the fuselage sides into the 1/4" ply plate, fill the hole with wood glue and drive in 1/8" dowels.

I really like your plan to combine the fabric-covered look with paint. Are you going with the original color scheme?

David