I use something very similar except I used the clear boxes and so didn't put the side wire in. They've worked great for two years. When they're very small I've had as many as 12 in there; as they grow I separate them out to other boxes in smaller groups until it's time for them to go outside. I don't want to have so many in there that someone will be forced to sit under the lamp because there's no room at the other side of the box. I too would remove the wire rack until they're a bit bigger.
Looks like a good job to me- now enjoy your new babies!
Looks like a good job to me- now enjoy your new babies!