how much paint do I need
2 gallons basecoat. Mix them together so they both match.
Want to have at least 2 quarts left over in case something happens to the car and you need to repaint the whole front or a complete side.
You want the color to match especially if it is a metallic. Nothing worse than a door repaint from a keyed scratch and it is the wrong color, sticking out like a sore thumb.
Good Luck on your paint job.