I don't think you should give them olive oil. I don't think they will benefit from it at all really but make there waterer really slippery. They need fresh clean water and putting any oil in it probably isn't going to be a good idea.
Like feathersnuggles said if you put anything you can put some Organic Apple Cider Vineger in there waterer but only if it is a plastic waterer. *Don't put ACV in metal containers*.
Chick starter feed would be the best thing to feed them and it is probably cheaper instead of buying everything to make your own. There are a lot of things in feed, not just wheat. Some have corn, soy, rice, millets, ect. plus all of the vitamines that they need. If you want more natural then they do have organic feed.
If the chicks are exposed to anything other then there chick starter then they need some grit. If you are going to be making there food then give them some grit seperately. I put mine in a seperate little feeder so they could get some when they needed it.