LOL nice dude, what year is that Nighthawk? mines an 82 that I'm currently working on bobbin. Gonna love seeing this project unfold!
As for the seat with the springs and hinge, I'm doing the same. It's a great idea, since i took out the air box in mine and I'm working on making a small "toolbox" that sits in where the air box use to be ( "toolbox" as in it could carry a few tall cans if need be lolz.) I'd say get rid of that air box for a cleaner look or sleeker since thats what your looking for, and move the electrical/battery inside or make a "stash" box >=D.