It's about 6hrs from Savannah(I-95) to Atlanta. I would suggest you go up I-75 to Atlanta(about 7hrs from Orlando), then resume your trip via either I-85N or I-20E to Augusta(about 3hrs) and joining I-95N. The new Georgia Aquarium is fabulous. Be sure you get advance purchase tickets, though--sometimes it's crowded and you don't want to be left high & dry with no tickets. Here's the link to the site: http://www.georgiaaquarium.org/.
There are several downtown hotels that border Centennial Park which are nice. The Park is fabulous in the summer--this is where the Olympics were and the dancing fountains are so fun for kids. CNN Center is down there too.