I have kept this colony for two months now, and here are some of my observations.
Diet
At the start, I only provided the colony with fresh leaves and fruits for food. I gathered all kinds of leaves from my yard as well as veggies from the store. Interestingly, the colony was not interested in rose leaves that multiple sources online say are Atta's favorite food. I suspect that this is because the rose leaves are too hard, and the young colony does not have enough large harvesters to cut the leaves. I gave them some other plants with hard leaves as well, and they are also ignored. The colony favored leaves from trees, that are of medium sturdiness. For fruits, the ants accepted most, but only small amounts each time. Orange rind was ignored, even though various online sources say they are a favorite. I suspect they are ignored for the same reason as rose leaves.
After a few weeks, I decided to provide the colony dried food, since I didn't want to go out and cut leaves everyday anymore. I gave them oats, dried rose petals, various seeds, grains and cereals. The colony loved all of them. In fact, the ants behaved like harvester ants and started to hoard the food. The food were collected and kept to the side. Most of the food were not in contact with the fungus. I think the ants had to manually chop up the food, and feed them to the fungus after. This behavior caused mold growth to explode, which is why I had to transfer them out of the soil nest. Interestingly, after dried food were made available, the ants have largely ignored all fresh food sources. At first I thought that the colony might be dying because they haven't touched any leaves, but I noticed that the fungus is still growing fast, so the dried food alone is enough for the colony.
After some research online, I found sources that say Atta choose their food depending on the humidity inside the nest. If the nest is too dry, they will only accept wet food, and vice versa. However, I don't think my setup is too wet. In fact, I think it is quite dry, because they only have a wet sponge and a cup of water inside the tank. I might buy a humidity sensor but I don't think they work well in high humidity environments anyways (All my humidity sensors never go above 80%). Either way, The colony is doing well. The fungus is growing fast, and I see a lot of brood. I will continue to feed the both fresh and dried food.
After placing the colony inside this bare container, the fungus has started to grow towards the wet sponge. I think this is because the sponge has a higher humidity, which is attractive to the colony. However this contradicts with the fact that the colony has only been providing dried food to the fungus.
A new brood chamber under construction. It's interesting that the brood is placed there before the chamber has been completed. Perhaps the fungus is not growing fast enough to fit all the new brood.
Interesting note - the rose petals that I use are from this rose tea package. The rose are supposed to be used for tea, and has a strong rose aroma. Because of this, there is now a strong rose aroma inside the nest, and I suspect the fungus has a strong aroma as well. Since the brood only eat the fungus, perhaps they will smell like rose as well when they eclose 
