How to paint hood?

I agree. Have it professionally done, it may be cheaper in the long run. If you must do it your self, you should remove the top layer of paint, as least to the primer. An orbital sander works very well for paint removal. You should re-prime it, and work your way down by grit size to about 600 grit, to get out all the scratches. It's then ready for paint. You could then take it to a body shop, and they could shoot it. Have you thought about a "satin black"? Easier to keep clean. Good luck. Howard