Which state decides federal policy on gay marriage for the military and in immigration, and for federal employees?
They have the power to control immigration policy. States decide their own policy on marriage, and military and federal employees have to comply with the laws of the state they're in. Being federal employees does not make them exempt from state laws.
States don't decide federal policy, and you knew that when you asked the question.
What enumerated power gives Congress the authority to control farming, manufacturing, and personal possesions?