Last summer I restored an old 78 Chevy 4wd pickup. I got the mechanicals done the sheet metal stripped of layers of old paint and fairly straight but summer ran out before I was really ready to paint.
So I used Rustoleum in approximately the final color and shot a mist coat plus two wet coats. The bulk of the truck was 1 part white, 1 part black and 2 parts silver for an approximation of a silver/gray. The color is OK, but the 'metallic' effect isn't as nice as what a real auto paint might produce.
It did take quite a lot more time to become 'tack free'. Knowing this I sprayed early in the day before the bugs come out in the evening. I was a little cavalier in getting the correct viscosity so got a bit more orange peel than I normally would like, but a quick wet sand with 800, 1000, 1500 then 2000 paper leveled it nicely and a rub out will give as much gloss as one would want.
I noticed that the red color was quite a bit more orange than the label on the can. I think the toxicity is a lot less than specially formulated auto paint as you can hardly smell the stuff, even when you lift your mask while spraying. With a properly set up HVLP gun, overspray and drift are almost non-existent.
I plan to block sand the body this summer to get it real smooth and straight. When time comes to choose the final paint, I may just stop off at Home Depot and use the savings for gas.