Quite the project, @gardengirlcanada. So many things to calculate and coordinate - I'm impressed! I'm sure you'll put it to good use.
I don't know if this will help with the air circulation in your build, but a guy I watch on YouTube just built a root cellar in his basement. He did a slick system with some vent piping that requires no power. The link leads to the first video on the entire playlist. The relevant ones are the last two. Maybe you can glean an idea or two from them.
Oh, and I do you hope you find a cute little window! That would be the icing on the cake!