Those septone paints from supercheap are not fantastic. Fine for painting parts in the engine bay etc but to paint the exterior of a car I would aim a little higher. Good quality paint is not that much to purchase. Black is hard to paint nicely too so I would be spending a lot of time on body prep (metallic black will show even slight imperfections), and spend some cash on a quality product from an automotive paint store.
Bad paint will piss you off every time you look at your car.