I would not change the aspect ratio on any images for the web. I think you want them to look as much as possible like your finished product, except much smaller for the web.
So I agree with your idea: "My logical idea would be to display the pics at their print size except in the case of assignments."
If the assignment photos look much different from the gallery prints, I would put them in separate sections of the website so each section looks internally consistent.
I look forward to seeing your site when it's up.
I think that must be right. If you change the aspect ratio, you change the crop, which presumably you have made exactly as you want it (while mentally apologising to Russ as you did) and hence which you don't want to change.
I join Eric in looking forward to seeing your site. Can I make an early plea for navigation using arrow keys?