Welcome to GA.

Be prepared to deal with rude motorists who are always in too much of a hurry.
There are many hills around the Atlanta area. If you don't want to ride in the traffic head out to Stone Mountain. Its a destination for hundreds of cyclists on the weekend and dozens of after work riders go there.
Many of the bike lanes really don't go anywhere. Some end at a shopping center or at the next intersection. Some of the "longer" bike lanes are used by local cyclists for training rides.
There are two good shops (IMHO) in the Duluth area -- CycleWorks and The Bicycle Wheel. I believe both shops host weekend and after work rides for riders of all abilities. If you ride with the faster groups they'll hit plenty of hills for you.