I assume you plan on letting them free range mostly, as opposed to being kept entirely penned up? If they free range, in a tropical climate such as yours, they will have a feast of vegetation and seeds and mostly bugs that they wouldn't need much in the way of chicken feed, maybe just enjoying some scratch grain occasionally.
If you pen them up in the run most of the time, they will be dependent on poultry grains, that's a balanced feed that has all the nutrients they would normally be getting if they free ranged.
So, the answer is, they will be able to be self sufficient when they are close to being full grown around six months old, to be safe, or around the time the first eggs appear. It's wise to keep them penned up until after they begin to lay anyway because they would be likely to lay every where but places easy to find the eggs. Penning them up gets them in the habit of laying in their egg nests.
At two weeks, they are still much too small to be able to find all the food they need for proper growth on their own. A mother hen usually teaches them about foraging for food, so they have to learn on their own, and that takes time. Besides, they are so little, they'd likely be picked off by cats, dogs, air predators mostly.
They will be happy to help you on your compost. Chickens adore digging in compost more than just about anything. Where is it you live?