Around here the most common unmedicated chick starter is Purina's Flock Raiser. One of our feed stores doesn't carry any unmedicated chick starter (except for really expensive organic), but they have an unmedicated 21% protein Meat Builder that would work just fine too. (I think it's only 1% higher in protein than Flock Raiser.) So there are a couple options anyway...
That's awesome! Broodies are such an easy way to raise chicks.
Once she's done hatching, momma will teach the little ones how and what to eat and drink, so as long as they have food and water available they will be fine.
Your picture is priceless! What an adorable little chick. Momma is gorgeous, too!