I would seriously consider giving them medicated chick starter right away. The medication in the starter helps them fend off coccidosis by weakening the parasite, thus letting their little systems grow strong enough to fight it off. Coccidosis is in the soil everywhere, and they will probably get it. If they do, and they have not been slowly built up with the chick starter, they will most likely die unless you use a strong medication.
I was worried about this too, but you take them off the chick starter way before you eat the eggs.
If you are going to keep them in a coop off the ground, however, it is not really a concern. You can also protect them from getting worms by keeping them in a coop, but they get bored.
As far as making your own food, be sure to grind it very well and mix in some grit so they won't starve. Glenda is right- they can't process food that is in chunks, and it could also get stuck in their crops and kill them. It all depends on how high a mortality rate you can live with. Some people prefer to go all natural, but the cost is losing more chickens. You must also supplement with vitamins.