Laminate afterwards -- Lamination films have quite a bit of stiffness when cold, but conforms and molds well when warm and bonds well when hot. applying it to the paper/foam first will affect how the board folds up, and can weaken the bond between the lamination and airframe as the parts try to slide relative to each other as they fold.
Spray adhesive is your call -- it's used to tack it down so it doesn't move until you've gotten the heat to it. As you turn the corners on the LE, a little bit of heat will make the plastic more flexible, so if you do use the spray, it's best to only hit the edge you're starting with, otherwise you'll end up with more wrinkles because it didn't want to turn the corners sharply when cold. Tack one side with glue/heat, gently pulling it tight, then spread the heat. The more you have adhered down, the less it will move.
I'd also recommend stripping the paper after assembling the wing halves and blunt-nose section. The lamination film will have far more stiffness and durability than the paper has, and you don't need the weight of both. You'll have to reattach the hatch and aileron hinges with tape, but that should be easy.
Naturally, I'd recommend trying all this on scraps first -- folded and glued into shape like a wing section, if you can manage it -- so you can get the feel of the material before you try it for real.
Hello Craftydan, you are the man! I could not hope for a clearer and more complete answer , so thank a lot for your complete and detailed post, I will just do as you suggested, and post the result