Is the aforementioned dream concerning the Prophet's teaching (peace be upon him) a specific formula for invoking blessings upon him authentic, and does it carry legal rulings, and is it considered a deception from Iblis?

The best forms of conveying blessings upon the Prophet, peace and blessings be upon him, are those he taught his companions, such as: "O Allah, bless Muhammad, Your servant and Your messenger, as You blessed Abraham, and bestow Your grace upon Muhammad and upon the family of Muhammad, as You bestowed Your grace upon Abraham and the family of Abraham." This is because the Prophet, peace and blessings be upon him, would not choose for himself anything but the best, and visions and dreams are not a source for deriving Islamic legal rulings.