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.
Cheaper then doing it yourself. Some would argue that if you're going to all the trouble to fully prep the car yourself, then why not just shoot the paint as well? Why get a shop involved? The answer is simply that you'll get a better job and for less money. Some would argue with this, but the fact is that if you've never sprayed a car before then your first car will have a steep, and expensive learning curve. Laying down an even, consistent coat of paint takes considerable practice. Also, paint and equipment is not cheap. You'll need to buy primer, color coat, clear coat, reducers & catalysts. None of these are inexpensive and you can easily spend as much in paint materials alone as the cheapest paint job at Maaco or similar shop.
What are the major color fields in the painting and their role in the entire composition? Is the light optically realistic or expressive as in Matisse's painting?
Definitely good inside the house is a new vinyl primer-sealer to be used as a base coat under any paint. It dries in as little as 30 minutes.
Better still, you don't have to spend hours getting ready and hours cleaning up afterward. Premixed paints, electric-drill attachments and self-dispensing calking guns make short work of preparation. Cleaning up is a soap-and-water job for the rubber paints, or a quick dip in special cleaners for the oils. Disposable dropcloths and paper paint pails are used once and thrown away.
Knock down texture is basically a orange peel that is sprayed on and allowed to "set-up" for a minute or two then gently "knocked down" by running a 6" drywall knife over it, "knocking down" the surface of the texture. Although knock down is a flattened version of orange peel, I suggest you do not use a spray can of orange peel, the knock down comes in its own spray can and the results are much better, again experiment before spraying it on the wall. However, If ever you apply any of the textures to the wall and are not satisfied with the results, wash the texture off immediately before it dries, then allow the wall to dry and try it again. Once you have the texture applied to your liking and you have allowed it to dry, you may want to paint the patches a couple of time before painting the entire wall, especially for walls where the paint to be applied will have some sheen. Multiple coats on these areas will make them blend in, unnoticeable, with the rest of the wall. You will know if the patches need more coats of paint, because the patch/texture will have absorbed the paint causing the spot to look duller than the rest of the existing wall.
But a Bogus Sample Card Equals Bogus Paint Colors. Of course, there's nothing wrong with stacking sample cards in the color wheel display so that the most attractive colors are the most visible. The problem occurs because so many of those bold, dramatic, "attractive" colors are basically useless as paint colors in your home!