One precaution: You can't paint with it in cold weather. The chemical reaction that transforms the water solution into a durable finish will not take place if the temperature is below 50°. (Conventional oil paints don't stick well in cold weather, either.)
Basically what you're looking for is a good, solid foundation of existing paint that is stable and still strongly bonded to the car. Many times an original factory paint job, even after decades will meet these criteria.
Special Surfaces. WHITEWASH. Whitewashes and lime paints must be thin when applied. In fact, best results will be obtained if the application is so thin that the surface to which it is applied may easily be seen through the film while it is wet. The coating will dry opaque, but two thin Coats will give better results than one thick coat.
The lite version of Galkyd is simply thinner. I use it more than the other. I love it. Paintings I did 16 years ago using Galkyds look as pristine as the day I painted them. You'll also need a canvas and some paint. I buy a tube of red, green, blue, purple, yellow, brown, white and black. I prefer what's called Ivory Black and a soft mixing white as you'll add white to a lot of different colors to make lighter versions. From these basic colors you can make any exotic color by mixing them in combination's. Be creative and experiment. And don't be afraid of color, because color is the most popular in museums! The bright paintings are historically the crowd favorites. As for color variety from these basic colors, mix red and white to make pink, mix yellow with green to make lime green, white with blue to make light blue, white with black to make gray, etc. Use your common sense and play with it! You'll also need pencils, an eraser and some Turpentine or Turpentine substitute. Keep your brushes soaking in it in a plastic cup to keep them clean and ready for your next color choice.... and to keep them from drying out.
If paints have been allowed to stand and hard lumps or skin have formed, the skin or scum should be removed, after which the paint can be stirred and strained through screen wire or through one or two thicknesses of cheesecloth.
Color can make a big difference in your life. I know from experience. Before I learned my right colors, I had a closet full of right and wrong colors. Of course, the colors did not work together and definitely did not coordinate. I had no idea of the difference that coordinated colors can make. Further, I had a drawer full of lipsticks some with gold undertones and some with blue undertones.
At a minimum you want to remove all the chrome from the car. Take off both front and rear bumpers. If your Mustang has bumperettes that are body color be sure to bring them along so they can get sprayed at the same time as the rest of the car. Remove all rocker, hood and trunk molding. Same for wheel well molding and all emblems. This would be a good time to order some new emblems and attachment hardware. Also spend some time cleaning up all the chrome with #0000 steel wool. Nothing looks worse on a fresh paint job then faded emblems and corroded, cloudy chrome.