Thats pretty cool! I've been thinking about doing something similar with a dark-activated switch (http://www.learningaboutelectronics.com/Articles/Dark-activated-switch.php) and an electric actuator.
Are the vent holes plugged? As they start to get closer to hatch the humidity should go up on its own as well caused by the chicks themselves. 65 % isnt danger zone, I wouldnt worry unless it goes below 60. Also how accurate is your hygrometer?
You could always use a regular fluorescent light if you are concerned about periods of light. Set it on a timer or control it by hand, they release minimal heat. Commercial brooders use a heating element on a thermostat and a small 6w red bulb for light and to attract them to the heat source.
Are these a commercial strain or heritage cross? We breed heritage crosses and I have never seen them be overly aggressive but the definitely do remind me of dinosaurs :)
We are looking for additional suppliers of Buff Orpington and Barred Rock hatching eggs. Our current supplier can't produce enough to keep up :) Must be NPIP, looking for another 4 dozen of each breed per week. You don't have to supply all needed yourself if you can't produce that many, I'll...
I would put a vent with louvers at the top back side of that design. Does the back drop down for easy cleaning? I would also recommend a sliding door for the coop / pen access so if you need to you can lock them in or out of the coop.
Read the instructions on the can, it may vary depending on concentration. Generally the powder is for where they do their dust baths and nesting boxes. As for the coop itself you should use the liquid spray and spray it down after cleaning.
It may be organically acceptable but its still a...