That's awesome. I remember our first egg like it was yesterday. (OK, so it was only 3 weeks ago) and today the second member of our chicken family (we have 7) laid her first. The other 5 are still holding out.
As for feed, I've been feeding ours Purina Omega-3 Layer from week 18. They're now 23 weeks. I use the same feed when they are foraging and wanting to scratch. I don't think "commercial" scratch feed has much in the way of nutrition for them, and they seem to eat all of the layer I throw on the ground for them, which I do 5 or 6 times a day. They love to crowd around my feet pecking up the pellets.
For treats, I try to make that good for them as well. They love cooked oatmeal,(cooled off of course) and will take meal worms, but their favorite is blue berries. I buy big bags of frozen berries from wally world. Try to hold the berries tight so they don't swallow them whole. It's much more fun, for us at least.