tophat, I think you've covered every question I could have thought to have asked in prep. Well done!
I've been helping teachers set up or fix aquariums in classrooms for years. The typical potential problems are fish outgrowing tanks, too hot or too cold, and lack of access to water supply to do water changes.
May I make a suggestion that might be a little easier for you? Have you considered an amphibian habitat instead of fully aquatic? The care is much easier, less demanding, the animals just as interesting... the only catch would be food supply. I had a lot of teachers who made the transition to amphibian habitats, the sacrafice being the weekly trip to the LFS for crickets, and all seemed to think it a fair trade.
My daughter is currently in the 6th grade, and when her friends come to the house, they like the fish, but are all instantly drawn to the salamander set up next to the fireplace. When I am done posting here I will go get a few pics of it and bring them back right away for you. My daughter can now name not only every common species of fish, but all of the plants in my salamander tank too. It's double the education! The filtration is easy, it's completely biological, sustains itself. Once/month I clean snail shells from the intake on the filter to keep the waterfall running, and when the water level drops I simply fill it up. I dump a dozen crickets in once/wk, and walk away. The light is on a timer. It doesn't get much easier.
Just something to think about, I'll be back with pictures in a few!