About Atlanta....its always something to think about whether driving a car or pulling the TT.
Best advice I've had: Drive straight THRU...don't get on the bypasses as those are HEAVILY used by locals. On Saturday, when you will be driving thru, and after leaving Holiday Travel Park (as an example...if you stay there): You will be FINE.
If you leave by 7am sat morn, you should hit Atlanta before Noon...and you will be FINE. Traffic, yes, always, but not bad. Again, STRAIGHT THRU. Use *511 on your cell for traffic info when in the area.
Coming home is the bigger issue, sometimes. Depending on what day you leave: Atlanta is farther north when leaving Orlando area, so you will hit it about 2pm. Again, STRAIGHT THRU is you best bet.
I mention STRAIGHT THRU ATLANTA several times: We would often take the bypass(s) around, as thats usually the best plan in a major city. Not Atlanta.
SUMMARY and ADVICE: Drive Straight thru atlanta your 2nd day on way to Ft. Wilderness.
Enjoy the Trip! It's not as bad as you think. It will be remembered FOREVER.
You might, either now or future, think about this: After leaving Ft. Wilderness, drive 400 miles or so to Topsail Hill Preserve State Park in Destin FL. Full Hookups, near the ocean. We do this every time we go to disney. Spend 2 full days there, and what a relaxing time after the hustle and bustle of DISNEY. White sand beaches, NOT crowded since Topsail is 10-12 miles from Destin center where EVERYONE goes to the beach. From there, take Rt. 331 to I-65, COMPLETELY AVOIDING ATLANTA on the way home.
Yes, this adds days to the trip...but the memories! Enjoy.