I am very new to this, but based on my short experience with young chicks, even a few chicks will outgrow that brooder quickly - and, given that it is indoors to begin with, I do think it will get quite hot inside the box unless (and maybe even it) you replace the plastic lid with a screen -if the lid has to keep a cat out, it won't have enough ventilation with just holes in plastic. My chicks are less than 3 weeks old, and when the garage is 60 degrees or more they hang out on top of or to the sides of the heating plate during the day, and I have it at almost maximum height - though it sinks into the wood shavings somewhat lowering the height. Another issue I might foresee is the water getting filled with shavings as the chicks start scratching. If you can get a nipple feeder, that has been a life-saver for me when I have to be gone for more than a few hours. I really think you need to have someone check the birds at least daily. I am certainly a bit too much a worrier, but I am having to clean out the waterers (which are raised on boards above the bedding) at least 3 times a day now, as they have really started scratching up a storm for their bedding and completely fill the troughs. That was not a problem when they were younger, though. [I know I need to work out something less labor intensive, but I'm not good at building elevated boxes and such, so I'm just looking forward to getting them to the coop.]