My good brother has one and has completed his DIY body work, sanded for days and has now purchased some emamel and clear coat. He wants to use my compressor with a gun or my cheap o Wagner electric spray gun to complete this task. Can I get some good advice on helping him with this project? What type of spray gun for my compressor is good enough (150 psi, 30 gallon)?

Unless you have a spray booth and the proper ventilation equipment this has to be one of the dumbest ideas on record. He has spent days sanding and prepping the body only to smear on a 50 cent paint job? Talk about turning a vehicle into a 50 dollar beater in a hurry. Since a paint job is the first thing a person looks at on a vehicle, why not spend the money on a quality job. Oh and let the body shop do the finish prep too.

Supply the paint and clear to Macco and I'll bet it comes out 10x better. (cheaply)

Thanks for informing me on how to get the best results, It's no question that it would turn out better but the issue is he has done all himself and wishes to continue doing so. So now perhaps someone can answer the question?

We did! But will try and answer it another way.
Most municipalities will not allow you to use paints with high VOC's in them without the proper equipment.
Automotive paints are very dangerous to work with. Flamability being only one aspect of the problem. The chemicals used as catalyst, hardeners, fish eye reducers etc,etc,etc are all hazardous to your health without proper safety equipment. Unless you have had proper training on their use, and have a complete and properly running spray booth it is probably illegal.
But if you insist, you will need a spray gun that can cost upward of 250 dollars and a compressor capable of producing large quantities of clean/dry air to supply that gun. You will need a place that is clean and completely dust free, you will need a complete bunny suit and respirator that has another method of supplying clean air to the face mask. And you will need years of experience using the equipment. Did I finally tell you how to do it?