The Tabernacle is at 152 Luckie St., Atlanta. It is downtown. Buckhead is about 10 miles. (I like to use mapquest.com to get driving directions from point A to point B.)
If you put downtown Atlanta hotel in the search box in the upper left of the page, reviews of downtown hotels and past discussions will come up.
As for walking in the area, I would take a cab if I were staying in the area. I suppose there will be a lot of people around as the show lets out but I would still not walk around.
When we go to downtown venues we get a room in another area and drive in. It means paying to park at the concert but it saves money because we generally can find less expensive hotels elsewhere. Also, you will have to pay around $15 to $20 a day at a downtown hotel to park. There isn't that much going on downtown in the evening besides not being safe to walk around.
As for recommendations of other areas, you will find a lot of recommendations by using the search box or reviewing the topic threads recently as there have been several discussions of whether to stay downtown as compared to somewhere else.
As for staying in the mountains, that is what I think you mean by a cabin, I'm sure you will get some good advice from others as well as their comments about staying near the concert.
Whatever you decide I certainly hope you have a good time.