Glueing balsa to foam
For that size plane, I would use 3M spray adhesive. It would work very well, it's basically dry to use, so it's instantly(almost) ready to keep working on and when you touch the sheeting to the cores, you better have them aligned well, it will be impossible to remove at that point. Not sure of the Titebond method, I've always used 3M with excellent results.
Good luck.