Hello Jason, Big welcome to Permies!
So the person you really need to talk with is Chris McClellan aka Uncle Mud who is the designer of the cottage rocket.
Perhaps he will see the bat signal and respond with all the answers you seek. In the meantime, I can give you my take on some of your inquiries.
So 1000 cubic feet is 10x10x10 feet. I would say this heater would be able to handle that size no problem.
As you can see in the photo, the rocket is elevated off the ground with bricks leaving plenty of air space to help vent heat from transferring to the floor. Being that your only going to have the stove running a few hours, this would probably be enough but certainly wouldn't hurt to have extra and also to monitor with a thermometer to ensure safety.
I know Chris has done many workshops teaching people how to build them and I think may even have more info on them if you check out his patron page at: Patreon.com/unclemud
or email at:
info@unclemud.com
Look forward to hearing of your upcoming adventures and please take lots of photos.