Being a body guy myself, not for a living but on the side, if you are going black, without a doubt and your mind isnt changing, I would definitely go with a PPG epoxy primer. DP90LF is the primer, it is black in color. Then it requires a catalyst. There are two types of catalyst you can use for this primer. One is a 401 and one is a 402. The 402 takes an activation time of 1hr. after you mix it you just stir every 15 min. until 1hr. passes then spray. It is very expensive but very very nice stuff. It is the best out right now in my opinion from PPG. As far as paint, I also have good luck with PPG. Just go with a two stage if you are just wanting a factory looking black.
You need a professional to assist you at least as you go, but as for sanding, I always start out with 120-220 grit depending on how much sanding needs to be done. The thing is, sometimes it takes rougher, this is where you need a professional to help. However you go about it, you will finally want to get down to a 400 grit before primer. Then after primer, wet sand with a 600 before paint. Again, this is just the basics and the way I do it. If the car needs body work, that is a whole other story. It really is more complicated than some like to make it if you want a NICE paint job. You need to at least talk several times with a local body guy to get his advise and help. You can save by doing the work yourself, but if you dont know what you are doing or at least had a hand in it before, you may get yourself in one BIG headache. Good Luck.