You scuff up existing paint for two reasons. First, you want to get rid of any oil, grease or dirt trapped in the top layer of paint. This is the stuff that cleaners and degreasers can't get off. The second reason to scuff is to set up a physical bond for the new primer and paint to adhere to. You want to give the old paint some tooth so the new sticks better. You'll need a large compressor, not just the typical 20 gallon variety most of us have. This is a 60 gallon, vertical compressor with typically a 5+ hp motor. Then you'll need a decent paint gun (possibly 2; one for primer and one for color) which again is an expense. Then there's the question of where you'll paint the car. Renting a paint booth is best, but can be expensive and hard to find. You can always seal up your garage or shoot out in the wetted down driveway, but you'll inevitably get dirt and moisture into the paint. 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?
Materials and their application, every paint manufacturers paint will vary. If you are freshening up old walls and painting back to the existing color, the product doesn't have to be high end or have good coverage. If you need to paint a dark color over light color or light color over dark, you may want to consider purchasing a top quality paint to avoid multiple coats. I suggest Valspar, Pittsburgh or Benjamin Moore top of the line wall paint. These brands work well for straight out of the bucket use and are application friendly. Sherwin Williams is not my first choice because the coverage is poor and you will have to apply multiple coats but, it does apply, fluently. If you find a product does not apply well, maybe it is to heavy and/or sagging on the wall, you may need to thin the paint with a little water, this will reduce the coverage but make the paint flow better and lay down nicer on the surface. I do recommend latex paints for all applications, these days a good high end latex is as good as oil paint and your tools clean up much easier, it will also be less harsh on the respiratory system. The only situation I recommend oil paint, is as a primer/stain blocker over stains that "bleed" through the paint. You can get a stain blocking oil primer in a convenient spray can and spot prime any trouble areas before painting and in the case you need to prime all of the wall due to smoke or water damage, I recommend getting it in gallons and rolling it on where the stains are present. Don't forget proper ventilation and/or a respirator when using the oil based primers! Airless Tip: If you have somebody who can start masking off the trim, have them start on that while you convert the airless to a new color. When changing colors with an airless paint sprayer it is a good idea to have a second bucket filled half way with clean water. Place the intake hose in the clean water gently without getting the old color everywhere in the water. Take the tip out of the airless and spray all of the old paint out of the hose and back into its original paint bucket. Be careful when doing this that you recognize when the paint starts turning watery. When it does point the gun into the first bucket and spray until it looks pretty clean. It doesn't need to be perfectly clean. When it looks good, clean off the intake line in the clean bucket and get the old color off the intake line. Now place the intake line inside of your new trim paint. Alkyd is an old interior paint made newly popular by a change in solvent - a super-refined petroleum chemical that has almost no odor. It is not a water paint. You thin it and clean brushes with mineral spirits or turpentine, or, if you want to retain the odorless feature, with the new odorless solvent. (Ask the paint-store man for just that, odorless solvent). Have plenty of newspaper around. After you clean your brushes wrap them in a plastic bag.