When you move in you can begin planting your "bones" of the garden! It will be the perfect time to put in trees and shrubs. The weather is also cool enough for you to ammend the soil if it is needed.
As for ammending, do a LOT early on. As soon as you can. At least double dig in whatever you can find: county compost, any kind of compost, or the more expensive Mr. Natural (which is fantastic stuff for either sandy or clay soil). Then you can plant away!

By heirlooms do you mean veggies, or flowering plants? Or both?

I like heirlooms a lot. I find that the heirlooms get less disease and I plant heirlooms (flowers and veggies) of all nationalities. Variety is the spice of life!! A local Atlanta woman, Lynn Coulter wrote a great book "Gardening with Heirloom Seeds".
There are many great plant choices for our area. UGA professors Michael Dirr and Allen Armitage have each written several books which include information about plants which survive heat and humidity. And if you like ornamental annuals, you can't miss the UGA web pages for trial gardens and Armitage's selections for "Athens Select" which do great here.

Here is a link that might be useful: UGA trial gardens

I like to start my seeds in a window box type planter. I do it outside, as soon as it warms up. I just don't have the right space and light to do it indoors. This year I have some hollyhocks and Salvia that are just about ready to go in the ground. But because of the drought conditions, I'm waiting.

I also collect seeds from plants in my garden and put them in the window boxes. Right now I have columbine and foxglove. I've had a lot of luck with the fox glove and have a few that have self seeded.

Start planning now for what you want to plant this fall/winter. As GGG said, that is the perfect time to plant trees and shrubs. You can probably get lots of trees 1/2 off in a few weeks and keep them in pots until then.

You may as well get a tiller or rent one and start amending away! Not sure what kind of soil you have in Lumpkin, but any soil can use some amending.

Make you set up pathways, rock walls, determine beds, work out any drainage issues, remove weeds (and some are tough to get rid of) and amend soil before planting anything.

Also put in any electrical lines or water lines first (even if they won't be hooked up to anything for a while). Trenching through tree and shrub roots or through paths later can really be unpleasant!