I do have a brooder plate I was thinking that would be safer. Just didn’t have room in the tote for it. We are still dipping down to below 0 at night, it’s currently feel like time of -14, that’s why I haven’t thought about putting them in the set up in my coop yet.I brooded my chicks outside in a wire dog crate. I lined the sides with cardboard to block drafts, added a MHP (heat source) and liberally added clean straw. They've done well with temps in the upper 20s (F).
I think you'll be fine. Be sure to have a lid and secure your heat lamp. A brooder plate or heating pad might be better.
Now...I'll sit back and let the experts reply.
by the way! I love your set up! we live in rural ND about 30 min from the Canadian boarder. this set up would scare me if we were to get a spring blizzardI brood outdoors in this structure: https://www.backyardchickens.com/articles/run-to-outdoor-brooder-conversion.76634/
Most brooder plates are made to function at temperatures above 50F. When it's cold, especially at night when the chicks are babies, I use a heat lamp to keep the area near the plate warm enough for the plate to function well then let the plate keep the chicks warm.
How big is the cage in question?
While the guidelines aren't as well established for chicks the best information I've come up with is:
1/2 square foot per chick for the first week or two,
1 square foot per chick for the next several weeks,
2 square feet per chick for a few weeks after that,
4 square feet per bird just like the adults after 8-12 weeks.
But after using a brooder shield for the first few days I give my chicks an area about 4x5 for another 5-7 days and then, once they're about 10 days old I give them the entire 4x8 area.
IMO, raising chicks in a roomy brooder so that they can get plenty of exercise gives you stronger chicks.
