You should get all your boarding pass to Jamaica when you check in. You can probably do it on line at home. You will get the return paper work when you check in for your return flight.
That will be plenty of time in Atlanta. You will have to take the train to the international gates but the signage is easy to follow.
We fly Delta out of MSP through Atlanta, never had a problem.
Your luggage will be easy to find once you're through immigration.
Relax and have a great time!
