Soft bathroom floor replacement

I would not use pressure treated plywood on the top layer. It is hazardous and vapors will permeate the vinyl into the living area. Cut everything as straight and square as possible. Use structural adhesive to attach the plywood to the supports, along with screws. I would use ridged foam board instead of all spray foam. Fit everything as close as possible before starting assembly. Use a toothed trowel to spread a foam compatible construction adhesive for the foam. I would use marine grade plywood for the top subfloor. Once you have it fitted, I would give it at least 2 coats of shellac to water seal it, so you do not have the same problem at a later date. I may catch flack for saying shellac, but it is the only finish that is water proof and will hold up.