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.
If you decide to do your own body work discuss it with the paint shop first. They'll probably have recommendations on the type of primer you use. Some brands will be more compatible with their primers or color coats. The rule of thumb is to stay within the same brand of paint, both for prep and color. Even the cheapest paint shops typically use a brand name on their intermediate and higher paint jobs. Find out what it is and use the same brand as your primer coat. This will ensure you don't create adhesion problems for yourself down the road.
The reasoning here is simple. Every color in the visible spectrum can be assigned a number based on a luminosity scale (a scale from light to dark) from 0 to 9 where white is 0 and black is 9. Now suppose that the brown you are trying to cover has a score of 8, and the yellow paint you want to apply has a 4.
Set up costs are normally included with any home improvement job, painting separate times for complete exterior painting can essentially cost double, unless agreed before work begins in painting quote.
Special paints have been innovated from different consumer insights and brilliant paint technology that allows specific paints for specific needs.
And if you are changing colors be sure you and the paint shop are crystal clear on what color they're going to spray. Never just describe the color. You won't get what you want. Guaranteed. If you're not using a factory original color then find out what kind of car the color you want came on. Give the shop a year, model and paint name and then insist on seeing a paint chip. Take the chip outside to see it in the sun light and verify that it's what you want. There's nothing more disappointing then spending all these hours and money only to watch your car come out of the shop the wrong color.
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!