You will want to know if there is frost depth required for GA , you can check this chart https://www.decks.com/deckbuilding/D...rost_Depth_Map
The treated posts that you have should have rows and rows of knife cuts on all four sides, that allows more treatment to enter the wood and would indicated that it is rated for underground service and concrete will not hurt it. It wouldn't hurt to wrap the post with with a blue skin like product to stop the wood from wick moisture into the wood.
If we were doing this here where I am well would have to have the bottom of the footing at 18" below finish grade and then a concrete wall on that to 6 or 8 inches above the same finish grade, that allow water that wicks up to dry to the outside.
If your floor is insulated, you want to vent the area. If you want to seal the area with poly up the walls then you want to condition the area like it is part of the house.