That looks good for one hen and her brood. I usually have one brood per pen, just in case the other birds decide to harm the young.
All you would need is a 60-100 watt light bulb 9-12 inches above the chicks to keep them warm. Be sure to place the bulb where the chicks can get away from the heat if they desire, but not too close to anything that may catch fire. "avoid putting water near the bulb".
First 3 weeks 100watt then a 60 watt until they leave the heatbox on their own. Throw away the bulbs at each increment to avoid the bulb from burning out on a new brood.
Putting an actual heat lamp is not needed sense it will be inside another building, and may burn the chicks and your brooder down.
They will stop making the edison type bulbs at the end of this year, so i have a stockpile.