I'm not an expert, but I can try to answer at least some of your questions.
1. First, what type of chicks are you raising? Meat birds? Layers?
If you are raising layers, they will need to stay on a chick starter, or starter/grower until around 18 weeks, or the first one lays an egg. Then you switch them to a layer feed. The calcium in layer feed is far too high for a chicks system to handle.
If they are Meat birds, then you should feed them a Meat Maker, or meat bird starter/grower until they are around 6 weeks old. Then you can either go the organic corn-fed way (which is what I plan to do) and feed them straight corn or scratch for the remaining 2-4 weeks until butcher.
2. Not sure if you meant treats, or that you want to mix your own feed, so I'll answer both.
Treats are just that, treats. They should be fed only in moderation, and whenever feeding the chicks anything other than their starter feed, you must also supply grit (playing sand works well for this, or some feed stores sell Chick Grit) so they can digest the treats.
If you meant mixing your own feed, as opposed to buying it at the store, I can help you there too because thats what I do! I am trying to raise them as Organically as possible as well, so I'll anser both of these below. We began changing their diet to one we mixed ourselves when they were roughly 6 weeks old.
3. Organic is the way to go, IMO, if you can. Keeping in mind that the innitial start up will be a bit more costly than buying a couple bags of normal chick starter/grower. I chose NOT to buy the bags of premixed, so-called "organic" feed mixes they have out there, as I wanted to be sure exactly what was in my chickens feed and mix it myself. You may chose to order from a company, or with a little effort and research, you can order your own ingredients and mix it yourself, as I have done.
We have our 8 week chicks on a mix that is 50/30/20 (or 50% chick starter/30% oats and grains/20% corn, and other supplements.
Here is our list of ingredients in our current feed:
starter crumble, alfalpha, wheat, peas, barley, oats, calcium, corn, coconut pulp, flax seed, linseeds, peanut and sesame meals, and natural vitamins.
I had to buy most of these in 25 or 50 lb bags, which made the upfront costs seem high. However, now that it is mixed I see the benefits in the chicks, and they out weigh the costs. Not to mention, I have enough feed to last me a LONG time!
I liked mixing my own because I knew exactly what I was putting in it and for what purpose. For example, the coconut pulp is high in fiber and protein. The Flax seed will increase the Omega 3's in their eggs (once they are laying). The oats help them to fill up and not grow quite so quickly, so they dont start laying before they are ready.
I also have a friend who does not eat meat, or anything that is raised on meat or meat by-products, but she does want eggs when I have them because I do not add any animal fat or animal by product proteins to their feed.
Finding the organic chick starter was the hardest part. Once they are 15-18 weeks, I can get rid of the starter, and feed mostly my own mix, and not need pellets or crumble at all and that will save time and money as well.
Oh, one last note, to go organic, you must stay away from chemicals, pesticidesm and medicated feeds as well. All of these will pass residues on to the eggs (once they are laying) and people buying Organic, wont buy them.