Here's how I would do it. You will need to prep the car like you would for a repaint.

It will need to be primed, since the paint is actually a high grade topcoat, and won't stick as well without it.

I would use a dark primer, so you don't have to shoot too many coats of black. (more coats = more dust)

Wet the floor to keep dust down, scuff sand, blow off, and tack.

The single stage urethane will have the reducer, and flattener added, and when that is mixed thoroughly, you will add the hardener.

Shoot at least two coats of the black mix. (You always do this with catalyzed paints, or they may not harden completely.) Stir it before spraying, each time.

If you get noticeable dust, let it flash off 30 minutes to an hour, scuff off the dust, tack, and shoot another coat overall.

The way it is sprayed, is the way it will stay. If you try to sand or buff, after it's painted, you will be able to see shiny or dull spots.

When you wash the car, rinse it off with water, to remove any "gritty" dirt, then wash with a soft sponge and mild dish soap. Rinse clean before it dries.