There are many different systems out there for spraying automotive paints but I will deal only with the system I have experience in. In the past I tried to spray a bike with a Wagner airless sprayer and rattle cans but nothing works like the correct equipment.
The most important piece of equipment is a professional respirator. These paints are highly toxic, highly flammable, and highly dangerous to your lungs. Buy a mask and cartridges that are specifically designed for painting. A dust mask won't cut it.
I use an HVLP (high volume low pressure) gun as it seems to get more paint on the paint surface rather than spraying loosing up to 30% of the paint as old guns used to. The gun has a small regulator that on the handle that keeps the incoming air supply at about 20 PSI. You will also need to rent or buy a compressor that can handle the output required by your gun. Check the documentation that comes with the gun.
Gun prices range from $60 to $300. I bought one for about $100 and it has done really well. Compressors are a great buy because they run so many tools that they can always be used when you are not spraying anything.