A--- The conjunction "and" suggests comparison and equality. So, one who says: "What Allah and you willed", compares the Will of Allah and the will If the slave, and puts them on equal terms. Whereas, he conjunction "then" suggests subordination and following. So, one who says: "What Allah then you willed" , he declares that the will of the slave is subordinate to and follow the Will of Allah Almighty. Almighty Allah says in His Glorious Qur'an, {But you cannot will, unless Allah wills}. AlInsan, 30)

And so are the rest of the aforementioned expressions!