I work with paint and coatings for a living, if your going to shoot(spray) auto paint then make sure you use a high quality respirator, yes you should use the hardener for the auto paint, and make sure you also apply only enough to cover the model, auto paint adds weight fast and you only need enough to get opacity(coverage).
if you are spraying blue, then a dark grey primer helps with coverage, spraying over a white surface requires you to use alot of material to get good color tone. primary colors like red,yellow,and blue, don't cover well in general.
having used toxic materials for many years I have almost totally switched to using water clean up paints
www.warbirdcolors.com paints are catalized urathanes, water clean up and vurtually no odor to speak of,great coverage with a small amount of paint, 8 drops of catalyst per oz. of paint and its fuel proof, I use it on all of my painted planes now.