OK i'm doing this right now (I can post pics if you want), I'm not going down to bare metal though so I started off with 220 and I'm finishing with 380, but if your going down to the metal then you should probably use at least something in the low hundreds. I also recommend that you use at least three different grits with the final grit being no lower then 300, the higher the final grit the better the paint job will look but it also takes a little longer, you must decide based on the quality of the paint that is on the car that this hood is going to and what quality you want the paint job on the hood to be. I have done three vehicles like this in the past and they have all turned out really well! When you are doing your middle grit make sure that there are no more rough spots left on the hood, at this point everything should be smooth and you shouldn't feel any bumps or divits as it will take forever to get them out with 300+ grits. Also with the heavier grits, it was mentioned before but I'll say it again, don't let the sander sit in one place, always be moving it and try and keep it as flat as possible against the metal. The car I'm doing now will be the first time spraying for me, this will be the hardest part, for if I screw up now i have to start all over!
P.S. Aucklands Grainger (sp?) sells automotive paint, primer, etc. etc.
You start with a bag full of luck and an empty bag of experience. The trick is to fill the bag of experience before you empty the bag of luck.