I use 30% turkey starter and I also add electrolytes to the water. 24% chick starter is generally accepted as the lowest protien you want to use. I typically lose 1-3 out of a hundred in the first day or two. Usually they're the last ones that hatched (smallest birds in the brooder) or ones that I assisted to hatch.....
That brooder is a tad on the small side. You're going to need second one for sure once the get bigger anyway. I use 55-gallon totes from home Depot. They are roughly 4ft x 20in and make excellent brooders. Here's a link to them....
https://www.backyardchickens.com/threads/diy-storage-tote-quail-chick-brooder.1247747/