So I don't see an answer to one of the original questions.
You are returning to the States and you have checked off that you have more than $10000 on your customs form. You have the form FinCEN 105 in your pocket.
You give the customs form to customs; they see that the box is checked "yes". Then what happens? Do the customs people ask for you to give them the form? And what kind of questions do they ask? Do they hassle you?
Thanks